Dan Lewis. 30 December 1910 −− 30 September...

2009 30 September−−Dan Lewis. 30 December 1910

Lorna A. Casselton and David A. Jones

originally published online February 22, 2012, 163-178, published 22 February 2012582012 Biogr. Mems Fell. R. Soc.

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Dan Lewis30 December 1910 — 30 september 2009

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Dan Lewis

30 December 1910 — 30 september 2009

elected FRs 1955

By Lorna a. CasseLton Frs1 and david a. Jones2

1Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK 2Gagle Brook House, Chesterton, Bicester OX26 1UF, UK

Dan Lewis is best known for his work on plant breeding systems. self-incompatibility is common in hermaphroditic plants as a mechanism that prevents inbreeding; it may be deter-mined by genes expressed in the haploid gametes (gametophytic) or by those expressed in the diploid tissue that gives rise to gametes (sporophytic). at different times in his career, Lewis contributed to a better understanding of both these systems, but it was his work on the gametophytic system in the evening primrose, Oenothera organensis, that broke new ground and enabled him to predict a molecular recognition between different proteins produced in the pollen and style; these proteins were encoded by tightly linked genes at a complex self-incompatibility (S) locus. Modern molecular techniques have since confirmed these predictions and revealed the actual nature of the proteins and their interactions. The research began as part of a programme of breeding plants of horticultural and agricultural importance while working at the John innes institute, the foremost place to study genetics in the UK at that time. The institution had william Bateson (FRs 1894) as its first direc-tor, followed by sir Daniel Hall (FRs 1909), who in turn was succeeded in 1939 by Cyril Darlington (FRs 1941). To begin your career there in the 1930s was almost guaranteed to lead to scientific success.

whereas much of his early work was with plants of horticultural importance, overall dur-ing his career Lewis worked with lettuces, apples, pears, plums, cherries, raspberries, toma-toes, roses, the evening primrose O. organensis, two tropical shrubs (Pemphis acidula and Cratoxylum formosum), Lantana, flax, oilseed rape, cabbages and radishes. He also initiated genetic studies with the inkcap fungus Coprinus lagopus (Coprinopsis cinerea).

His greatest strength was in bringing together the current scientific thinking of the day, and he wrote and lectured on both eukaryotic and microbial genetics. On the basis of his direct experience of flowering plants and fungi, he published several influential reviews, in particular in 1954 an outstanding review entitled Comparative incompatibility

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166 Biographical Memoirs

in angiosperms and fungi (14)*. This was declared a Citation Classic in two different series of Current Contents.

Dan Lewis was elected a Fellow of the Royal society in 1955. He became Quain Professor of Botany at University College London (UCL) in 1957, and was President of the Genetics society from 1968 to 1971.

earLy LiFe

Dan Lewis was born at Basford, stoke-on-Trent, the son of ernest and edith Lewis. His father’s family was originally from wales, but his grandfather, who began work as a gentle-man’s gardener, had moved to the potteries where he started a wholesale grocery business—Dan Lewis and sons Ltd of shelton. He had eight children; ernest albert Lewis, Dan’s father, was the seventh child. ernest succeeded his father as a director and secretary of the business in 1910, the year in which Dan was born. ernest had four children, Dan’s elder sister, Dora, who was an accomplished musician, and a younger brother, Clifford, who had a twin who died early in childhood. The family was relatively affluent and lived at Basford Villa, a substantial family house with a fine garden.

Dan attended newcastle-under-Lyme High school from 1919 to 1929. From the ages of 9 years until he was 15 years old, his passion was to construct and experiment with simple electrical and radio apparatus. in 1920 he read that alfred P. Morgan’s The boy electrician was to be published in england in July. aged 9½ years he managed to persuade a local bookseller to let him buy it a week or so early. This well-used copy of the book still exists but now needs to be held together by elastic bands. Using his telephones and radios he could communicate with a friend several houses away. at that time coils had to be hand-made because they were not available commercially.

More often than not he was in the lower half of the class. when it mattered, however, he showed his ability in the school Certificate examination of 1928 with one distinction, three credits and two passes. Having come top in science and French he gained a prize. His spare time was spent with his bicycle and his friends with like interests. at that time he was not particularly interested in sports, but his close friend norman Carter, the son of the chief of police, was a runner, and he secretly trained Dan to run with him in the early mornings. To the amazement of the school, Dan ran and finished second to his friend in the mile in 1927 and broke the school record in 1928.

it seems that part of the reason for his lack of academic success early in his school life was his interest—and single-mindedness to the exclusion of much else—in electricity and associated physics. He once asked his sister to write a poem for his school homework while he got on with more interesting things, and was duly embarrassed when it won a prize. His enthusiasm and academic competence so impressed his physics teacher, Mr G. H. Clough, that he was urged to go to Cambridge to read physics. Just before his last term at school, however, he went on a cycling tour of Devon and Cornwall, and during that time his brother contracted scarlet fever. Dan was not allowed home because he would have been quarantined and unable to go back to school. He was sent to stay with a Mr wooding, a pottery designer, enthusiastic

* numbers in this form refer to the bibliography at the end of the text.



Dan Lewis 167

gardener and charismatic teacher who lived in the same village. Over a period of six weeks he was introduced to horticulture, and this proved critical in determining the future course of his career. The school had not taught biology, so this was a whole new experience for him. To the dismay of Mr Clough, he changed his allegiance from physics to plants.

Dan’s father was very supportive of his son’s decision. The practical side of horticul-ture appealed to Dan, so he sought a ‘hands-on’ professional training. On leaving school at 18 years of age he spent a period of 2½ years at the nurseries of R. G. James near Crewe, at Treseder’s (then in Truro), and finally at the Hillier nurseries. The Cornish experience was frustrating because he was sent out as a salesman for much of the time: his pay at £1.00 per week made him very cheap labour. while in Cornwall he corresponded prolifically with his father. in a letter of 30 november 1930 he wrote:

i am now studying Darwin’s Origin of Species. i started it six months ago, but found it above my head, but now i am easily understanding it. it is quite the best reasoned and most enlighten-ing book i have read. He must have been a wonderful observer of natural things and also a very methodical noter of all he saw. His statements are all backed up by two or three verbal illustrations and facts.

in 1930 his ambition was ‘to get to Kew and if i show enough ability and keenness, might get onto the staff.’ although he did not pursue this aim, he was eventually offered a job at Kew—that of director! He declined. This was in 1969 when he was Professor of Botany at UCL. He would have had to resign from the University Grants Committee, the advisory committee of the British government, which at that time advised on the distribution of grant funding among the British universities and of which he was chair of biology. He believed that this committee gave him a much greater influence on British biology than being director of Kew; furthermore, at Kew he would have been obliged to work and live under the flight path to Heathrow airport.

while at the Hillier nurseries, Lewis realized that to progress further in horticulture he needed to get a degree. He took a correspondence course in biology offered by wolsey Hall in Oxford to get the necessary qualifications. Because of its strong focus on horticulture and agri-culture, he chose to go to the University of Reading. He arrived in 1932 and very soon met Mary Phoebe eleanor Burry, who had graduated in zoology some years earlier and was studying for an Msc as well as supervising a dormitory. in the December of the following year they were mar-ried, a marriage that lasted 70 years. Dan read botany, chemistry and physics for his degree and obtained second-class honours in both the General and special Degree categories. although his academic studies in botany were influenced by Professor J. Matthews and Professor T. M. Harris (FRs 1948), it was the mycologist Dr C. Terence ingold, later Professor of Botany at Birkbeck College, London, who stimulated his interest in genetics and physiology.

sCientiFiC Career

The John Innes Institute (JI), 1936–57On graduation he had been awarded a research scholarship by the University of Reading and began some research on the absorption of solutes by leaves, the subject of his first publication (1). He soon realized that this work would not take him far. in the summer of 1934 he had attended a summer course given by C. D. Darlington and J. B. s. Haldane FRs at the John




innes Horticultural institution, then in Merton Park in surrey. when he saw an advertisement for assistant Pomologist at the Ji, he immediately applied and became one of the first research employees to be appointed almost directly after his first degree. He was appointed assistant to Morley Crane (FRs 1947), who led the fruit breeding work at the Ji and who was particularly interested in the genetics of self-incompatibility in fruit trees.

His first assignment was to analyse a mass of genetic data collected by Crane and w. J. C. Lawrence on the inheritance of different characteristics in raspberries, such as male sterility and leaf shape. Lewis learned his genetics from these studies, and the data enabled him to define at least two linkage groups and to publish two papers describing them (2, 3). The rasp-berry work also formed the basis of his thesis presented to the University of London in 1939 for the award of a PhD.

Having mapped a gene for male sterility in raspberries, he became interested in how impor-tant such mutations might be in wild populations. in 1941 and 1942 he published two papers on male sterility (4, 5), which turned out to be classics. what interested him was that although male sterility caused by a nuclear gene mutation could arise, particularly in inbred lines, in natural gynodioecious populations in which both female and hermaphrodite plants are found growing together in equilibrium, male sterility is determined cytoplasmically. His calculations showed that nuclear mutants had little chance of survival in wild populations and that for male sterility to be an effective breeding system it was essential that this be determined by a cytoplasmic factor (gene).

in the early years his research covered the basic genetics of apples and pears as well as raspberries. He went on to study the physiological effects of temperature on self-incompat-ibility in various plants grown at the Ji; in particular he was interested in how temperature affected pollen tube growth in compatible and incompatible fertilizations (6). Controlling the temperature accurately required good thermostats (figure 1), and these had to be made by hand. The hand that made them at the Ji belonged to a member of the legendary Fabergé

Figure 1. apparatus used to control temperature during flower bud development. Designed by H. Osterstock at the Ji in Merton Park.



Dan Lewis 169

family. Carl Fabergé was an extremely gifted technician and it was possible to put glass thermostats over branches and maintain any temperature that was chosen. Lewis also studied the effect of polyploidy on compatibility and fruit production and the effect of chemical treat-ments such as β-naphthalene acetic acid, which proved a powerful parthenocarpic stimulant in some plants, inducing fruit development in the absence of pollination (7). all of this was relevant to successful plant breeding.

at Merton there had been a long-running programme of research on the two types of prim-rose—pin and thrum (distyly)—which was a classic example of sporophytic incompatibility, with thrum pollen fertilizing the ovules of pin flowers and pin pollen fertilizing the ovules of thrum flowers, although this is not always absolute as was shown in the original studies by Charles Darwin. Lewis contributed to this programme with his physiological studies on another distylic species, Linum grandifolium, in which he showed that the underlying mecha-nism relied on an osmotic interaction between pollen and stigma (7). Pollen grains failed to swell and germinate in pin × pin pollinations, and pollen tubes burst in thrum × thrum pollina-tions. This became a classic study that he wrote up for School Science Review in 1948 (10).

Lewis always said that the joy of working at the Ji in his early days was the confidence that the senior staff had in junior members and the freedom they were given to do what they wanted. it was this, he said, that led to wonderful science. This freedom allowed work on plants that had no direct horticultural importance provided that they could be used to answer fundamental biological questions. included in many of Lewis’s studies on temperature, poly-ploidy and chemical treatments was the evening primrose, O. organensis. sterling emerson had previously shown (emerson 1938) that a small population of O. organensis from the Organ Mountains of new Mexico contained exceptionally large numbers of alleles of the self-incompatibility genes (S genes). work on O. organensis was being conducted by another young recruit at the Ji who had been appointed to the staff at much the same time as Lewis: Geoffrey Beale (FRs 1959) (Preer & Tait 2011). They both saw the potential of this plant as a model organism for the study of incompatibility because it would be easier to work with than a tree. He and Beale initially joined forces but Beale had to leave the Ji when he was called up for military service in 1941, and it was left to Lewis to demonstrate the true potential of this plant as a model system for investigating how the S genes control self-incompatibility.

Most of the staff at the Ji were exempt from military service because their work was con-sidered to be in the national interest. However, Lewis did do his bit. During the war years he lived with his wife and daughter, Hazel, in a small cottage in Ockley in surrey, and there he became a member of the Home Guard. He can be seen fifth from the left in the back row in the photograph of his platoon (figure 2).

in the late 1930s Lewis was corresponding with s. emerson, then at California institute of Technology (Caltech), about his ideas for using O. organensis for research on incompatibility, and emerson confirmed that it would be good material because it was easy to follow pollen tube growth in the style. This was perfect for detecting mutations in the S genes that conferred self-compatibility. in 1946 he published the first paper (8) on S gene mutation in which he was able to provide evidence that the S locus was complex and that there were two genes, one acting in the pollen and the other in the style. self-set seed after X-ray treatment gave rise to plants that produced pollen able to fertilize both mutant and parent plants—the pollen was self-fertile. in reciprocal crosses, however, with the mutant gene present in the style, pollen with the parental S allele was incompatible and the mutant allele retained its parent specificity. The mutation was therefore in the gene acting in the pollen but not in the gene acting in the




style. He elaborated this experiment in papers published between 1948 and 1951 (11–13). The style is a sensitive sieve for allowing only compatible pollen to grow and fertilize the ovules—Lewis estimated that the style of O. organensis could sieve some 6000 pollen grains. He was able to detect self-compatible mutations (produced either spontaneously or by X-rays on pollen developing in buds) by observing the growth of pollen tubes in the style—screening as many as 200 styles a day and determining from the number of pollen tubes at what stage in pollen development the self-compatible mutation had occurred. He could moreover make assessments of the mutation rates in the S alleles. To estimate the amount of self-set seed was initially more difficult. There seemed to be a minimum number of fertilized ovules within a capsule to permit that capsule to swell and allow seed development. This is where his experi-ments with β-naphthalene acetic acid were important: after treatment, capsules with very few fertilized ovules, or only one, would swell and produce seed.

it is significant that every self-compatible S gene mutation that he analysed had lost spe-cificity; not one was found with changed specificity. To this day, no new S alleles in any plant have been generated from pre-existing alleles, and how they arise in the wild is still a matter of speculation.

Running in parallel with the O. organensis experiments were similar experiments with cherries, which had a similar gametophytic incompatibility system. self-compatible cherry trees would have important commercial consequences. self-incompatibility meant that it was necessary to plant mixed orchards to get good fruit yields. with self-fertility this would no longer be necessary. By X-raying cherry buds he successfully ‘crossed’ emperor Francis with Bigarreau napoleon, two varieties that are not compatible. any cherry produced should have resulted from a self-compatible mutation in the pollen. He planted out more than 2000 seedlings derived from this cross and was confidently expecting to be able to develop the first

Figure 2. eastern Command Home Guard, 7th surrey (Ockley) Battalion, ‘F’ Company, during world war ii. Back row, left to right: Bill Tickner, Les sands, [unidentified], edwin Coldman, Dan Lewis, Bill Hazeltine, [unidenti-fied], Bert ansell, Frank Dawson, Charles Chilvers. Front row, left to right: Lt wood, Ron wootton (Company sergeant Major), [unidentified], Chris Millet, [unidentified], Major wooldridge, [unidentified], Bob Bravery.



Dan Lewis 171

self-fertile cherry varieties (figure 3). in another experiment reported in 1947 (9), he took a full-grown cherry tree and had it caged before the winter together with a hive of bees. some 50 000 flowers were produced in the following spring, and an estimated total of 60 million pollen grains were sieved by the styles of these to give 30 self-set cherries!

His work on cherries was, however, thwarted. The Ji estate at Merton became limited by urban housing and in 1945, with the help of the Ministry of agriculture, the Trustees bought a mansion and surrounding 372 acres of land at Bayfordbury in Hertfordshire, and many of the staff were installed in purpose-built houses round Broad Green, close to the laboratories.

The move took place in september 1949 and Lewis became head of the Genetics Department. Unfortunately, with the move, work on cherry trees came to a halt because the government refused to support it. He was astonished. The possible saviour of cherry growing in the UK was to be ‘thrown on the compost heap’. at least one of these self-fertile ‘seed-lings’ arrived with a breeder in Canada. There it was crossed with the north american variety Lambert. a selection was later marketed as the first self-compatible cherry variety—stella. Most garden centres in the UK now stock stella.

after the move to Bayfordbury, Lewis continued work on O. organensis and other plants but looked for a new model system in which to study self-incompatibility. He chose the ink cap mush-room Coprinus lagopus (now Coprinopsis cinerea). it was well known that mushroom fungi had multiallelic self-incompatibility (mating type) genes, and his plan was to select for mutations that conferred an altered specificity in much the same way as he had done in O. organensis, again with the expectation that new alleles would be detected. There are no publications from this period but the 1954 Ji report described experiments by Lewis and Lesley Crowe on reciprocal crosses in the fungus that could be used to demonstrate cytoplasmic inheritance. importantly, he spent the next year (1955–56) at Caltech on a Rothschild Fellowship, where he worked in the laboratory of George Beadle (ForMemRs 1960), whose nobel-prizewinning work with the fungus Neurospora crassa had established the one enzyme–one gene hypothesis. Lewis took

Figure 3. Lewis sampling cherry flowers with Miss irena Modlibowska at the Ji in Merton Park in the mid 1940s.




C. cinerea strains with him and, working with Beadle’s former student norman Horowitz, suc-ceeded in isolating several biochemical (auxotrophic) and morphological mutants that provided the basis for future genetic analysis with the mushroom.

His return to the Ji coincided with the return of Peter Day, who had worked with him at Merton several years before. Day had been in the Usa working with pathogenic fungi, but he enthusiastically joined forces to develop the genetics of C. cinerea at Bayfordbury. Their inter-ests were complementary. Day was interested in how the incompatibility (mating type) genes regulated sexual development, whereas Lewis was interested in detecting mutations in the genes themselves. although Lewis was to be unsuccessful in this, together with Day and Crowe he initiated studies that made the fungus a useful genetic model that is still studied worldwide.

During his year at Caltech, Lewis had received an invitation from the Provost of UCL, sir ifor evans, inviting him to become Quain Professor and Head of the Botany Department. it took a year to finalize acceptable conditions for him to move to UCL, one stumbling block being where he would have land to grow plants. This was resolved after much hunting by his being given facilities at nuffield Lodge in Regent’s Park. He had helped to establish a strong research interest in fungal genetics at the Ji and, after he left, it remained pre-eminent with Peter Day continuing the work on incompatibility in C. cinerea, and John Fincham (FRs 1969) and Robin Holliday (FRs 1976) doing some of their seminal work there.

University College London, 1957–77Lewis was the first geneticist to be appointed head of one of the University of London’s several botany departments. Genetics was increasingly being seen as central to biology, some-thing that had been appreciated by the Provost when inviting him to UCL. His predecessor, the distinguished ecologist william Pearsall FRs, had created a world-class botany department but genetics had not been one of his priorities. in his very first academic term Lewis intro-duced and taught a basic course in genetics for a combined class of first-year and second-year undergraduates. He also introduced third-year students to fungal genetics in practical classes.

in 1963 he oversaw the move of the Botany Department from its old site above the slade school of art (which it occasionally flooded) to the purpose-built Darwin Building in Gower street that was designed to house many of the different biological sciences departments at UCL. The building was officially opened in 1964 by the then President of the Royal society, sir Howard Florey, and this was celebrated by all departments with displays and demon-strations that highlighted the wonderful state-of-the-art research facilities that the building housed.

Lewis had been invited to the University of California at Berkeley for six months in 1961 to teach, and during this time he was won over by the american modular degree structure. On his return he joined forces with other senior academics at the University of London who were looking for a move from strictly department-based teaching programmes to a course unit sys-tem that would allow students more flexibility in the subjects they could choose to put together for a Bsc degree. He was very active in getting the ‘new’ modular degree accepted throughout the university, despite the initial reluctance on the part of sir ifor evans, who rapidly changed his mind when Lewis threatened to resign if he would not give the go-ahead! The modern facilities and equipment of the Darwin Building were a fitting start to the ‘new’ Bsc degree when it was introduced in 1966.

with the move to the Darwin Building, Lewis was already active in modernizing and expanding the teaching in the Botany Department, a response to what he called the ‘golden



Dan Lewis 173

age’ of unification of the biological sciences (17). a new foundation course for first-year stu-dents was introduced that included cell structure and function, metabolism and genetics. all students took the same first-year courses but new courses were introduced within the depart-ment that enabled them to choose between a degree in botany and one in microbiology. The Botany Department continued to have a distinguished tradition in ecology, and another new development was the introduction of an Msc degree in conservation.

Lewis’s own research laboratory in the Botany Department focused on C. cinerea, and he brought with him from Bayfordbury a large collection of auxotrophic mutants and wild-type strains of different origins. He was amazed to discover a real bonus in the dirty air of London—there was little contamination of cultures and one could leave Petri dish covers off for extended periods while working under the microscope.

Having failed to obtain mutations in the incompatibility genes of C. cinerea, his interest turned to using mutation to gain a better understanding of the nature of the gene itself and how the expression of genes was regulated. This period coincided with the exciting discoveries on gene regulation in bacteria and bacterial viruses that culminated in the award of the nobel Prize in Physiology or Medicine to the French scientists Jacob, Lwoff and Monod in 1965. Fungi were being seen as important eukaryotic models for similar studies. His first publication on C. cinerea was a study of suppressor gene mutations that showed unexpected properties. although these mutations were recessive, they failed to complement despite being located in widely separated different genes (15).

it seemed possible at the time that the way in which genetic tests were being conducted might be affecting the complementation results. Basidiomycete fungi do not normally form somatic diploids when mated like budding yeast, but instead they form a dikaryotic mycelium in which nuclei from the different haploid mates remain separated in each cell. although each cell is equivalent to a diploid cell, in which different alleles of a gene are present, the alleles are present in different nuclei. By questioning whether complementation tests in the dikaryon were reliable, a strategy for forming somatic diploids was developed by one of his research students (Casselton). it turned out that complementation tests in dikaryons were reliable (18) although nuclear separation could result in a ‘leaky’ gene expression of the recessive mutation. However, it was a useful technique that enabled diploid–dikaryon comparisons to uncover some unexpected gene interactions with mutants resistant to an amino acid analogue (26) and to explore the effect of ploidy on incompatibility. These years at UCL saw many of the techniques for working with C. cinerea being refined and improvements being made to the linkage maps (23).

His interest in using amino acid analogues to select for mutations would certainly have been stimulated by the work of his colleague in the Botany Department, Leslie (later sir Leslie) Fowden (FRs 1964), who had shown that many plants accumulate analogues of protein amino acids but are themselves resistant to the normally toxic effects of these compounds. Fungi were seen as ideal genetic systems for investigating how such resistance could be achieved because it was possible to show growth inhibition in the presence of the analogue and then to select for rare resistant colonies produced on growth medium containing toxic levels of the analogue. Lewis focused studies of his laboratory on ethionine and parafluorophenylalanine, thereby adding to a growing literature that he reviewed together with his colleagues Fowden and Harry Tristram in 1967 (19).

analysis of one of the mutants resistant to ethionine was particularly interesting because it identified a gene that encoded one of the activating enzymes (transfer Rna synthetases)




required to transfer an amino acid to its relevant tRna for incorporation into protein. The mutation resulted in a change of function rather than a loss of function, enabling the enzyme to discriminate between the normal amino acid methionine and its toxic analogue. This paper was published in Nature in 1963 (16), next to a paper by Peter Peterson and Fowden that demonstrated a similar control of resistance to a proline analogue in a higher plant. in another study, analogue resistance was the likely result of a breakdown in regulation (loss of feedback inhibition) resulting in overproduction of the normal amino acid and thus dilution of the toxic analogue. Philippa Talmud and Lewis (24) revisited the question of what made amino acid analogues toxic and showed that p-fluorophenylalanine and ethionine were highly mutagenic in themselves. This could be measured by the increase in frequency of mutations predicted to result from single-nucleotide changes in Dna. interestingly, the analogues seemed to act differently, one by being incorporated into proteins and the other by causing ethylation rather than methylation of Dna.

Lewis continued to take an interest in higher plant incompatibility. at nuffield Lodge he was able to grow O. organensis and later Raphanus, Brassica, Nicotiana and Pemphis. He continued to write reviews, some on plant incompatibility systems but also others incorporat-ing newly emerging discoveries of the time, of which he always kept abreast, and to which he had ideas to contribute.

in 1970 he spent three months as a Royal society Leverhulme Visiting Professor at the University of singapore and by chance his interest in distylic plant incompatibility was rekindled. He loved to teach and, naturally, he included a short course on breeding systems in higher plants. This proved topical and relevant. The Department of Botany organized day trips into Malaysia to look at the local flora, and Lewis was delighted to find Pemphis acidula growing in the wild. what was interesting was that P. acidula was recorded as being distylic (like primroses), but belongs to a family (Lythraceae) that typically have tristylic flowers (flowers with tall, mid or short styles and correspondingly placed anthers). Together with the Professor of Botany at singapore, a. n. Rao, he studied three different populations of P. acidula and found that although the population was strictly divided into plants with long-styled or short-styled flowers, all the flowers had, in addition to the appropriately placed anthers, a third whorl of anthers slightly above or below the mid level, reminiscent of tristyly. He was able to show that present-day populations of P. acidula are derived from tristylic plants and adjustment to distyly is still going on (20). Completion of this process is prevented by ‘disruptive selection’ (first described by Kenneth (later sir Kenneth) Mather FRs (Mather 1955)) because selection for the right pollen size is opposed by selection for the right anther height. a much more extensive plant hunt for P. acidula, again funded by the Royal society, was conducted a few years later. This trip took him to the east coast of africa including the islands of Madagascar, aldabra, several islands in the indian Ocean, Taiwan and the norfolk islands in the Pacific Ocean, where the plant populations he found confirmed his original con-clusions (25). sampling plants on deserted shorelines was not without danger. at one point, in Tanzania, he was mugged and found himself with a knife to his throat while Phoebe was forced to hand over all their valuables. in telling this story he was always full of praise for the courage Phoebe had shown. He lost all his samples on this occasion and afterwards they took the precaution of having an armed guard with them.

in London he began to take an interest in the multiallelic sporophytic incompatibility sys-tem using Raphanus, a member of the Brassicaceae. He was convinced that in this system, as in the gametophytic system he had studied at the Ji, there must be more than one gene at the



Dan Lewis 175

S locus and that there was an interaction between pollen and stylar proteins encoded by these. His prediction was correct but the mechanism could not have been resolved by the techniques then available. Hugh Dickinson was working with him at this time and elucidated the cell biology of the self-incompatibility response by electron microscopy, showing that pollen coat proteins were both necessary and sufficient for this response without pollen tubes penetrating the style (21, 22). we now know that the incompatible interaction is between a ligand in the pollen coat and a receptor in the style activating a downstream signal transduction pathway (reviewed recently by Chapman & Goring (2010)).

Those who worked with Dan Lewis will remember his overwhelming enthusiasm for sci-ence and his constant encouragement in the laboratory. He loved a party, and he and Phoebe were wonderful hosts, inviting students and staff to their home in Canonbury and bringing a level of social cohesiveness to the department that had been missing before he came. He loved adventure too. His enjoyment of teaching took him to Delhi on a Royal society Leverhulme Visiting Professorship in 1965. He had a Triumph Herald car shipped to india so that he and Phoebe could visit the sites during their visit, but they then drove this small car home through Pakistan, iran, Turkey—where most of the roads were rough—and then on through europe. They had many adventures on the way. They spent a night in an iranian police station because they could not find anywhere else to stay. They wondered why the bed was suspended from the ceiling rather than standing on legs but realized during the night that it was to stop the cockroaches that were then covering the floor from getting into bed with them. They had a shattered windscreen in Turkey that was cleverly replaced with 5 cm strips of glass. Miraculously, the only puncture they got was on an autoroute in France!

aFter UCL

early in a retirement that lasted 31 years, Lewis was invited to be a Visiting Professor in the Biology school at Queen Mary and westfield College (now Queen Mary, University of London) by the head of the school, alan Bevan. He maintained his interest in higher-plant incompatibility systems, writing reviews and co-authoring papers on Brassica and Raphanus with one of his long-term collaborators M. i. Zuberi. By this time he and his wife had sold their large house and moved to a flat in Myddelton square in islington. These were the years when he would start the day at the swimming baths perfecting his crawl, and well into his eighties could still swim his age in lengths of the pool. aged 80 years he swam 5000 m in a charity event.

His passion for plants never left him. Before he retired, he and Phoebe bought a country home at Long Lanes (Hermitage) near newbury and this is where they escaped every weekend. They created a wonderful garden (figure 4), and Lewis had the joy of growing his vegetables as well as cultivating a vast array of ornamental plants, on most of which they were expert, and some of which had been grown from seeds collected on his travels. He delighted in exhibiting at the local flower and vegetable show, especially when his onions won first prize.

The last six months of 2003 were the saddest of his life. in July 2003 he fell over while chopping wood for the fire and broke his hip, and this meant that their country life had to come to an end. although they were both in their London home on 27 December, their 70th wedding anniversary, the celebrations were very muted and tinged with acute sadness. Phoebe had a recurrence of bowel cancer and was terminally ill. she died on the last day of the year.




Lewis was immensely proud of his daughter, Hazel, who took a degree in physiology at UCL and made her career in biomedical research. He revelled in his three grandchildren and especially in his great-grandchildren. The eldest, also Dan, had difficulty in saying ‘great-grandfather Dan’ and so called him ‘Great Dan’, a tribute that he relished. Hazel’s husband, David Jones, was appointed Professor of Genetics at the University of Hull in 1973, something Dan Lewis claimed he had nothing to do with! in 1992, at the age of 82 years, he and David published a review on the genetics of heterostyly (27). in this they attempted to trace all the papers in which the genetics of distyly and tristyly had been clearly established.

Music was very important in his life. He had been brought up in a musical household, and as a young man he played the clarinet. no doubt this helped when he was courting his future wife Phoebe, who played the cello in the University of Reading orchestra. There was always a piano in the house and he loved to play Beethoven sonatas. His love of Mozart was legendary. He cer-tainly made an effort to collect recordings of everything Mozart wrote—whether or not he suc-ceeded we do not know. He particularly loved the Mozart operas, and he and Phoebe regularly went to the Royal Opera House and to Glyndebourne when they were performed. Phoebe organ-ized a party at UCL for his 80th birthday, and one of the gifts presented by his former colleagues in the Botany Department was a facsimile copy of a Mozart piano concerto. Harry Tristram set him a musical puzzle to accompany this gift. He photocopied part of Köchel’s catalogue of Mozart’s work showing the opening of K80. To everyone’s amusement, Lewis needed help to solve this puzzle, not recognizing the connection between the Köchel number and his age! after Phoebe died, music was a great solace. He was confined to his London flat with declining mobil-ity. For the final five years he had a devoted live-in carer in esline sibanda. He was taken ill at home in september 2009 and spent the last 10 days of his life in University College Hospital, where esline and Hazel visited every day to make sure he was comfortable.

Figure 4. Dan Lewis in his Long Lanes garden with his wife, Phoebe, and daughter, Hazel, in 1991. (Photograph taken by David Jones.) (Online version in colour.)



Dan Lewis 177

degrees

1939 PhD, University of London1951 Dsc, University of London

aCknowLedgements

Family letters and memories have contributed much to this biography and given us unique access to the influences that shaped Dan Lewis’s early career. He left a detailed archive of scientific papers and official letters that have been invaluable. we are grateful to former colleagues, namely Professor Peter Day, Harry Tristram, Professor Hugh Dickinson and Professor Philippa Talmud for reviewing and contributing their thoughts on his professional life at the Ji and UCL. Professor Deborah Charlesworth FRs kindly added her professional comments on his scientific achievements. sarah wilmot was helpful in confirming relevant details from the archives of the John innes Centre, and Briony Thomas researched the names of the men of the Home Guard in figure 2.

The frontispiece photograph was taken in 1955 by L. s. Clarke and is from the John innes archives courtesy of the John innes Foundation.

reFerenCes to other aUthors

Chapman, L. a. & Goring, D. R. 2010 Pollen–pistil interactions regulating successful fertilization in the Brassicaceae. J. Exp. Bot. 61, 1887–1999.

emerson, s. H. 1938 The genetics of self-incompatibility in Oenothera organensis. Genetics 23, 190–202.Mather, K. 1955 Polymorphism as an outcome of disruptive selection. Evolution 9, 52–61.Preer, J. R. & Tait, a. 2011 Geoffrey Herbert Beale MBe, 11 June 1913 – 16 October 2009. Biogr. Mems Fell. R.

Soc. 57, 45–62.

BiBLiography

The following publications are those referred to directly in the text. a full bibliography is available as electronic supplementary material at http://dx.doi.org/10.1098/rsbm.2011.0023 or via http://rsbm.royalsocietypublishing.org.

(1) 1936 a note on the absorption of solutes by leaves. J. Pomol. Hort. Sci. 14, 367–379.(2) 1939 Genetical studies in cultivated raspberries. 1. inheritance and linkage. J. Genet. 38, 367–379.(3) 1940 Genetical studies in cultivated raspberries. 2. selective fertilization. Genetics 25, 278–286.(4) 1941 Male sterility in natural populations of hermaphrodite plants. New Phytol. 40, 56–63.(5) 1942 The evolution of sex in flowering plants. Biol. Rev. 17, 46–67.(6) The physiology of incompatibility in plants. 1. The effect of temperature. Proc. R. Soc. Lond. B 131,

13–26.(7) 1943 The physiology of incompatibility in plants. 2. Linum grandiflorum. Ann. Bot. 7, 115–122.(8) 1946 Useful X-ray mutations in plants. Nature 158, 519–520.(9) 1947 splitting the gene. Discovery 8, 168–173.(10) 1948 Pollen-tubes, incompatibility and osmotic pressure in plants. School Sci. Rev. 108, 206–212.(11) structure of the incompatibility gene. 1. spontaneous mutation rate. Heredity 2, 219–236.(12) 1949 structure of the incompatibility gene. 2. induced mutation rate. Heredity 3, 339–355.(13) 1951 structure of the incompatibility gene. 3. Types of spontaneous and induced mutation. Heredity 5,

399–414.


http://dx.doi.org/10.1098/rsbm.2011.0023

http://rsbm.royalsocietypublishing.org



(14) 1954 Comparative incompatibility in angiosperms and fungi. Adv. Genet. 6, 235–285.(15) 1961 Genetical analysis of methionine suppressors in Coprinus. Genet. Res. Camb. 2, 141–155.(16) 1963 structural gene for the methionine-activating enzyme and its mutation as a cause of resistance to

ethionine. Nature 200, 151–154.(17) 1965 a golden age. The Times supplement on University College London, p. vi.(18) 1967 (with L. a. Casselton) Dilution of gene products in the cytoplasm of heterokaryons in Coprinus lago-

pus. Genet. Res. 9, 63–71.(19) (with L. Fowden & H. Tristram) Toxic amino acids: their action as antimetabolites. Adv. Enzymol. 29,

89–163.(20) 1971 (with a. n. Rao) evolution of dimorphism and population polymorphism in Pemphis acidula Forst.

Proc. R. Soc. Lond. B 178, 79–94.(21) 1973 (with H. G. Dickinson) Cytochemical and ultrastructural differences between intraspecific compatible

and incompatible pollinations in Raphanus. Proc. R. Soc. Lond. B 183, 21–38.(22) (with H. G. Dickinson) The formation of the tryphine coating the pollen grains of Raphanus, its prop-

erties relating to the self- incompatibility system. Proc. R. Soc. Lond. B 184, 149–165.(23) 1974 (with J. north) Linkage maps of Coprinus lagopus. in Handbook of microbiology, vol. 4 (Microbial

metabolism, genetics and immunology) (ed. a. i. Laskin & H. a. Lechevalier), pp. 691–699. Cleveland, OH: Chemical Rubber Company.

(24) (with P. J. Talmud) The mutagenicity of amino acid analogues in Coprinus lagopus. Genet. Res. 23, 47–61.

(25) 1975 Heteromorphic incompatibility system under disruptive selection. Proc. R. Soc. Lond. B 188, 247–256.

(26) (with s. senathirajah) Resistance to amino acid analogues in Coprinus: dominance modifier genes and dominance reversal in dikaryons and diploids. Genet. Res. 25, 95–107.

(27) 1992 (with D. a. Jones) The genetics of heterostyly. in Evolution and function of heterostyly (Monographs on Theoretical and applied Genetics, no. 15) (ed. s. C. H. Barrett), pp. 129–150. Berlin: springer.



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