111. Account of a MicroJropical ImeJigahn of fmcrd Species ofpoffen, with Remarks and tue/ionr on /he SlmBurc and U'fi of that part of Vcgctablcs. By Luke Hward, EA. of PIaflow in EJex. 1 -

Read March 4, r8oo.

I N the Spring of 1795, having much leifure, I devoted a portion of it to the ixamination'of various minute produktions of Nature in a good compound microfcope. Thefe refearches would probably have terminated in prefent information and amufement only, but that [hey were accidentally turned to the pollen .of flowers, re- fpeaing which, as a botanifi, I found an inclination to inform my- felf, by comparing the feveral fpecies together,

I began my obfervitions with the Hazel-tree, Corylur AvcZlana. On a calm dry day I ihook off fome of the pollen from the expanded catkins upon a clean piece of writingpaper. I alfo gathered foma of the catkins and female buds. Thefe I viewed feparately oil a clear plate of glafs, ufually tranfmitting the light through them from a ipeculum below, and with different magnifying powers, prefer- ring thofe which, without en'ormoufly enlarghg theabjeBs, gave a clear view of the firufiure and poiltion of feveral a t once. - As 1 purfued this method with the reit I examined, I mention this to Cave repetition,, and ha l l give the appearances from notes made at the time.

I . Cor-/US Avelfana. . Anthers furniihcd with tranfparent horn- Pollen crumbles from the furfa'ce, and is fome-

Gmes fo ahindant as t'o fall in a viGble cloud on the flightefl motion VOL. VI. K of

. fike appendages.

66 Mr. HOWARD'S Account f a Micro/copicdl Inu@sath

of a branch. T o the naked cye it is a fine yellow powder. A fcw grains laid on the glafs plate and viewed with the lens No. 4, foma. appear of an irregular angular fiape, opake, cxccpt in one or two parts, where light Fafing prefcnts the appearance of a perforation; others nearly fpherical, the furface divided by depreired lines into a number of convex facets. T h e tranfparcncy. of thefe i s fuQ, that they r c f l d the image o f ' a fmall objeA held under them, as well as a drop of liquid. On repeatirigthe examination, the former are found to come from the mofi mature anthers, and to differ from t h e latter only as.a raifin does fmm a grape.

A clear drop of diitilled water being put on the glafs, both kinds imbibe it with the avidity of a fponge; at the fame time difienditig and fpreading abroad in the water, but without any mot-ion further than that which this expanfiou caufes. W h e n f a t u r a t d with water. they remain a: the bottom, dear as the liquid itfelf, and all alike dillended to a bulk many times greater than their original one. in the dry flate. T h e y are now feen to be mult$&cular capfules, hav- ing fepta in various diteltions within them, the union of which with thc'cxternal membrane appears at the angfes in thedry itate, and at the cieprefkd lines in the wet.

Thefe capfiiles may be kept in the water for feveral days without any further pcrceptible change. W h e n that is dricd u p they return to the o p k e h t c , and-the fame operation may be fevcral times re- pcated on them.

In exhibiting this fpeEtacle to fome friends, pnre water not being juir at hand, a drop of brandy was fubfiituted for it. T h i s gave rife to a phaenomenon cqually curious and unexpelted. The grains cxpand,.as in water; hut in t h e nreaii time they are put iiltc r:!pid motion, each grain darting from Gde to fide with the vivacity of a {warm of p a t s in the air. As they approach'tocomplete expailGm the motion.dies away, and one after another finks to the bottom.

By.

of fmcral Species f Poflett. 67

%y a fmall addition of frelh brandy 'fornc few arc cscitcd a fccoiid $ime, but with fainter movements. P d e n t l y the liquid Ocgins to ;be obfcured, and in a few minutes the grains are motlly difperfed and decompoUed,-and thc fpkit, exhaling, leaves a fort of c x t r a n on the glafs mixed with very minute undlrolved partklcs; smoiig

w h i c h fometimes appear a fcw unbroken grains, much changed, arid now refembling an empty bladdcr lying flat.

Anthers capfular, bearing thc. pollen on their inncr furface, and difcharging it by a britk explofion from an aper- ture on the tide next the pifiil. I f tlieJtkma be touched with a piti 'at a certain period of the infforefcencc, it- happens commonly tha t all the anthers projea h e i r poiltn a t once ; and it may thus be colle&eci 011 paper. T h e proper time for this is whcn the Jigma is elevated a little from between t h e anthers. In fize and hruature this pol- l en nearly rcfcm'bles the preceding, and is, in like manner, capablc of imbibing water and difperfing with a rapid motion in fpirit.

2. Erica cclmen.

3. Rcfcda odorata. Mignonette. Unripe pollen, firooth, egg-oblong, tranfparent, without fepta ?

In water it expands to a fphere, and is a&ed upon by @it as the ~ preceding.

4. :CattusJugc/Iformis. Creeping Cereus. Anthers oblonz, crumbling. Pollen of a large fize, compared with

any others I have iPen i in h a p e refembling a plump grain of wheat, whi te and di'iphanous. It cxpaiids in water to a ihape ncarIy Cphe- rical. T h e contat1 of fpirit brings on a pearly opacity. T h c p i l l s

imbibe it flowly, and during expalifion revalve on their axes with a pretty regular motion, exhibiting a fpekiacle no lefs novel than &- l ighthl. In thc mean titnc, fome minute particles are feen to bc ejekied, atid, the motion ceafing, the tranfparency returns, procecding from the furface to the centre. *

K z If

68 Mr . HOW A R D 'S Accotrnr of a Mcro/ccpical ZnvcJigurion

If a . piItil be f'eparatetl from tlic expanded flower with grains of pollen adhering td it, the lattcr will be fouud already expanded to a fpheroid. Cover the whole with a drop of fpirit on the glals, the piitil is not afferocd in any way, but fome of the grains quit it and. revolve on their axes. W h e n thcfe arc exhaufied, the addition of more fpirit excites others: after a few minutes, fonie of thole firit excited begin to put oiit a fniall thread, which gradually elongating, '

t he grain din)iqilhes in proportion, until it is entirely drawn out into a vermicular fibre, which again is prefently difipated into par- ticles too minute to be feeti in 'the now opake medium. T h e liquor from the tube of the pifiil, and a fofution of fugar in water, were all'o found to produce this evolution in very mature grains from the anther. , It alfo fometimes takes place in the twinkling of 81) eye, fo as to be fcarcely traced in fome few grains out of a number put into fpirit at once. Thofe which have been fome time in contaa with the piitil are always 'rnofi fliiggiih in their evo- l u tion.

5. Carex acuia. Anthers oblong, crumbling. Pollen angular, opake, with apparent

perforations. I t dilates in fpirit a i d remains ftationary, but ejeas numerous minute particles in rapid focCefion from its furface. IVhen it has become tranlparent i t appears as if filled with feeds.

T h e preceding may fcrve for examples of thefe phznomena ;* but there was not one among the various ipecies I examined, which did not exhibit them in a greater 01: lefs degree. Yet various other parts of the flower, immerled in fpirit under the microkope, did not be- tray the fmallcfi veitige of them.

T h e proper fpirit for this purpole f e e m to be a m.ixture of onc part pure fpirit of wine with two of water. A fironger fpirit, or even fpirit of wine alone, may fometimes be required when we ope- rate upon a pollen which has, by any means, become previoufly

fat u r a t ed 6

bf fmral Spccica L$ PoUen. 69

faturated with . rnoiiture, (ar has lolt, by keeping, a part of its irri- tability ?) but it does not enter the dry grains ,h readily as water alone.

1 have fince CubjeEted pollen to examination in feveral of the moIt itimulaiit oily and faline liquids, but have not been able to perceive that any of them had a Gmilar eKe& on it.

I t is propcr here to remark that the utinofi care is requifite to prevent accidcrt@ mixtures of the fubjeEts or menftrua in theie ex- periments, which might greatly embarrafs and miflead the obferver. Separate pieces of clear glafs for the feveral kinds, and feparate pointed glafs , tu~m~Q a ~ n v t i y t ~ ~ ~ ~ w i ~ - ~ ~ e r c t + u e be reqiiiite. I t will be proper attentively to examine thgmUen?dry, a8 w4 as.the liquids, before they are uled, in order to be fatisfied of the abfence of animalcules and other extraneous matters which might be iuf- peaed to infldence the appearances.

I do not pretend to Cay that the above-related experiments were abfolutely free from optical deception ; but I may venture to affirm, from frequent repetition of thcm, that, when tried with due pre- caution, they will fcarcely evcr be found to fail of producing the appcaranccs related.

-Engagements of fuperior importance a t prefent prevent, and may long continue to prevent, my pulhl'ng thele inquiries much further. I t i s for this realoir, and be&ufe:I I b ~ W m p l ~ i P Eeeing it done by Come perlon more cap i t&WM~~lng&m.wi th due ex- aAnefs, and drawing ixoper inferences from them, that I am willing .to make them known in their prefent jmperfea fiatc. For the afliitance of thofe who may incline to prokccute the fubjefi, I ihall now itate the amount of the preient dikovery, and the hints for further invcfiigation which have occurred to me.

Should it*be found, on repeating ahd extending thefe oblerva- tion s,

76 MY. HOW RD'S Acetini f a il&croJcopicnl Inu$igeiicn

tion$, h a t the pollen of vegetables is in, d l cafes fimilarly a A d upon by uratcr and by fpirit.oE wine,.it will follow,-

I. T h a t each grain of pollcn iii ' the anther is an organic body, varioufly conltrulted in*various fpecies, and containing.

u VeKels or pores capable of imbibing water, of difiending thereby and co'ntraQing again whcn itquits thcm ; in w h c h particulars they refemble ipongc, &c.

b A parenchyma, confilting of Come fubfiance @f greater fpecific gravity than water, and infoluble therein), which is emitted with a greater or kfs degree of hfce whetr thc fiimulus of alcohol; is. applied to the abibrbent veffels. Th i s fubfiance is cither in part folub!e in alcohol, or the grains contain

c An effential oil or relin, to which they owe their colour and d o u r .

2. T h a t there exifis in the grains of pollen, in a very eminent degree, .that?proptrty af vegetables called irritability, which they are capable of retaining for a certain time after feparation from the anther.

3. That alcohol is the p6per flimulus by which this irritability nlay bc excited, and the texture of the pollen in Come manner dcve- l o p d in conlquence thereof. I prefer this method of accourltiiig for the appearances tha t take place when the pollen is immerfed in fpirit to another tha t might bc fuppoicd on chemical principles, beingaffurert,, &ht any one who has once isi'peccted the proccfs wlll be Gtisfied tha t 'fomething more than mere lolution or chemical decofipofition t a k s place therein, and that thc vital principle of the pollen is t he chief agent.

The liquor From the tube of the piltil and the folution offugar were, indeed, found to bring on the evdution of the pollen of Cd,#fu~

figel. in a flower mannec than lpirit; but when w e confider how ipe ed i lp

of Jcvctal Spcies of Pollen. 71

fpeedily fuch matters pafs into the vinaua itate, it fecms p ~ a b l e t h a t both of thcfc might contain alcohol. Yet, it is alco pofible that fomething common to this latter fubftance, with the 'faccha- rinc matter it is producible from, may bc the real exciting caufe.

T h e cxifience of abforbent veirels in the pollen is proved by the change of form, increafed tranfparency, and great dittention pro- duced by the water. I t is rcmarkable, that complete faturation u f d l y brings the grains near to a fpherical Ihape, however remote froin it their original me.

I t iecms necefidry t o fuppofe the parenchyma for the follo\ving reafons. Something is evidently given out to the fpirit beforc thc diCperGoii of the grain commences. I n fome cafes this is viGble in minute particles moving about in the drop ; in others it is difcover- able by the tinge on the dried $ace, and by the itriae which eppear when more fpirit is adrted. Now, if the grains contlted merely of the vegetable fibre formed into vcficlcs or cells, their tcxture.would no moi-c be deltroyed by fpirit thar. by water, and the penetration of the watcr wbdd produce the fame motions as tha t of the $Kit. But if w c fuppofe that, in proportion as the i'pirir pesetrates the feveraI parts of there curious capfulcs, fomc tranfparent 'fubltance is forcibly expelled froin thcrn ; the various motions into which they are thrown will be eafily explained by the recoil of the grain in the oppofite dire&ion. €t will hence appear why the pollen of I.

which fecms to canfiff of many kparate cells, is driven alternately in all direaions by thcir fuccefiive difcharge, and why that of 4*- which is a long tube rolIed up, and probably with but one orifice, is thrown into a rotatory motion. T h e opacity of.tljis Cpecies during the difchargc may be attributed to the evacuation of this canal, and the returning tranfparency to thc cl~trarice of the fpirit into it from the abforbent veKelG, or at the orifice. I do not remember to

have

72 Mr. HOWARD% Account of a Microfiepr'cal InvcJligation

have feen a fin$ bubble of air efcape from the grains of pollen in the whole courfe of my obfervations. As thcir texture was in many cafes quite defiroyed, if it had been porous, as that of dry ~ o o d , &c. air mult have appeared. I therefore conclude them perfealy folid in the dty itate.

I think it pofible that the profecution of thefe inquiries by means of the microfcope, may throw fome light on the obfcure fubjea of vegetabk reproduEtioa ; may teach us why the anther is almofi always expofed to the air for fome time prtvioua to the dif- charge of the pollen, and this even in, aquatic plants ; as dlfo what is the office of that lacchanne liquor with which the itigma is fur- niflied, and of which fuch a fiore is fometimes provided in the nefiary. T h e very manner in which the impregnation takes place may pollibly be learned by attentive oblervation.

'rile Gmilarity of the unfoided pollen of No. + to the form of the plant it comes from, might furiiiih matter for fpeculation; but I decline this, believing that experiment and careful ohfervatiori mufi always precede found theory.

Reflelting on fome of the propertics of pollen in which it bcars a refcmblance to itarch, I was led -to examine that alfo in a fimildr manner, and was not difappointed to find its itru&ure the fame, Starch confilts of homogeneom p i n s or capfules ihaped like No. 3. capable of imbibing watcr u i th jncreafe of bulk and tranfparency, and of rcturning to their original fiate on ,parting with it. They are alfo difpded, with more or Lds of motion, in fpirit; but in t l j i s particular different fpcciinens were found to vary, which may be attributcd to difference in age or foundnefs. If a little M heat flour be mixed n*ith water a:id ipread on the glafs, thefe grains ap- ):ear in grc<it abund;~nce, mixed with fibrous mattcr. Other kitids 0 1 grain affoidcd thc iame reiult, with a difference in the form of

the

. ' '

of Jeverd Sjkcicr of Polen.

rht capiults. As the vcgetable facculum, which confifis entirely of this kind of matter fcparated from the foluble and fibrous part, has been long confidered as the fame fiibftance, though obtainable from different parts of vegetables, I extended the inquiry to tuberous . . roots, and obtained a further confirmation of the identity of pollen and fzculum. A potatoe feems to be almofi nothing e lk but' an airemblage of grains of fiiculum, with their interltices occu$cd the juice. If this root be boiled or baked until it becgmes mqali, the juice will no longcr be found; and we might be at a If fo know wliat was become of it, if the microfcope did not h o w t at it has entered into the grains of fzcduin, which are thereby greatly difiended, as is, indeed, evident to the naked eye.. The vital principle is thus deitroyed ; for thefe bloated grains will not move in Ipirits, but give out a tin&ture to it like other dead matter. By thiserneans, and the 10fs of folidity, they are prepared for more eafy decompofition in the itomach.

If water containing it be made to boil, it becomes ajelly. I do not apprehend that a true fo1ution takes place even in this cafe. It appears that the fame effe& is produced on the grains by the heat as by fpirit of wine. They are difperfed into very minute particles; and the furface being thus multiplied, a greater degree of attranion takes place between the ftarch and the water, and the former remains fufpnded.

Starch is abfolutely infoluble in water.

It appears to me to be worthy of future inquiry, 1. In what parts of vegetables in general the pollen or fzculum

is to be found. 2. In what refpeas that which is iccreted on the anther differs

from that which is contained in the root, feed, or fap. In the leaf, petal, bulb, fibrc of the root, or other parts already brought to per- fe&ion, I am inclined, from fome obfervation, to think it will not be met with.

V O L . Vf. L 3. Whether I

74 3. Whether the germ or embryo of the feed, previous to the im-

pregnation, contains it. In what manner the pollen of plants in general will be aAed

upon by theliquor from the neOary, when eqofed to it in circum- fiances fimikir to thofe of Exp. +

5. And laitly, to inveitigate the varieties in form and k u a u r e of the different ipecies of pollen; and to examine how far they agree or differ iu the feveral fpecies of each genus, and genera of each natural order.

Mr, -UOWARD'S Account of a Micr6/copical Invfligotion, &c,