THE MAGAZINE

OF

NATURAL HISTORY.

MARCH, 1829.

ART. I. An Account of Mr. Needham's original Discovery of the Action of the Pollen of Plants; with Observations on the supposed Existence of active Molecules in Mineral Substances. By ROBERT BAKEWELL, Esq.

Sir,

THE accounts which have been recently published on the action of the pollen of plants, and particularly Mr. Robert Brown's observations on this subject, and on the general existence of active molecules in organic and inorganic matter, have excited much attention among the naturalists of our own country, and on the Continent.

After my return from Hampshire in October last, I put my microscopes in requisition, to examine some of the extraordinary phenomena described by Mr. Brown. The season being far advanced, my garden did not furnish many species of flowers, but sufficient to confirm some of the facts stated by Mr. Brown, and to present others, not less curious, which are not described by him. While engaged in amusing myself with these microscopic researches, I found, behind a neglected corner of my book-shelves, an octavo volume, uncut, entitled, An Account of some Microscopic Discoveries. These discoveries are detailed, under different heads, in the titlepage: among others are, "Observations on the Farina fœcundans of Plants, with a new discovery and description of the action of those minute bodies analogous to that of the calmar's milt-vessels, and an examination of the pistil, uterus, and stamina of several flowers, with an attempt to show how the seed is impregnated." The work was published in 1745, and is signed T. N. On perusing it, I find that the author was Mr. Needham, to whom Mr. Brown refers, as having obscurely seen the motion of the particles of pollen. I suppose Mr. Brown had not met with this volume, which I believe is scarce; for VOL. II. No. 6.

B

Mr. Needham has not only minutely and accurately described the action of the pollen, but has correctly delineated it in the act of ejecting the particles contained within it. He also mentions having seen the particles move when within the pollen of the pumpion. He appears, indeed, to have described most of the principal facts, respecting the action of pollen, that have yet been satisfactorily ascertained. As similar microscopic observations at present engage the attention of many distinguished naturalists on the Continent, it is but justice to our own countryman, Mr. Needham, to bring forward the discoveries which he made near a century ago. An account of his work cannot fail to be acceptable to many of your readers.

In order that those who are not at present acquainted with vegetable physiology may have a clear notion of Mr. Needham's discoveries, it may not be improper to state that the farina, or pollen, of plants, is that fine powder which may be observed within many flowers, and is particularly abundant in the white lily, where it occurs in the form of an orangecoloured meal. This powder is supposed to perform the important function of impregnating the seed. When seen through a microscope, as Miss Kent well describes, in p. 232. of your useful Magazine, "every particle appears a little bag, containing a meal yet finer."

Pollen is generally translucent, and the smaller particles may be seen within, like the seeds of a white currant, but much smaller in proportion. The grains of the pollen of the geranium are oval, and do not exceed the 400th part of an inch in diameter, as I ascertained by a micrometer scale; the particles or granules within it do not exceed the 10,000th part of an inch. The pollen of some plants, as the mallow and hollyhock, is surrounded by minute spines, and, when magnified, the grains resemble the seeds of cleavers or goose grass (Gàlium Aparìne). Mr. Needham, as will be shortly shown, was the first who discovered the internal particles in the grains of pollen, and attributed to them the property of impregnating the seeds of plants.

The first sixty pages of Mr. Needham's work contains an account of his discoveries of the structure of the animalcules in the milt-vessels of the calmar, a species of cuttle-fish. His object is to prove that these minute animalcules have an internal organisation, resembling a pump and sucker, and contain within them" opaque globules, in a kind of serous liquor," nearly similar to what he afterwards discovered in the pollen of plants; and he considers these internal particles to be in both cases the real fecundising agents. The succeeding twenty

four pages contain his discovery of the action of the pollen of plants when placed in water. This action, he says, "had escaped the observation of all naturalists till that time, as appears by their express assertions; for they affirm that water causes no alteration in the farina." His observations appear to have been made in the warm climate of Portugal, where the action of the pollen was vigorous and rapid. Mr. Needham says, "The farina of the Lilium flòre reflexo was the first in which I discovered the action of the globules; for, upon viewing it in water, I thought I perceived some alteration in these minute bodies, as if the shell, or case, had emitted through a small aperture a train of minute globules, which appeared but as points in the microscope, involved in a filmy substance, as the eggs of some aquatic insects are, and, in effect, not much unlike them. I immediately applied some fresh farina; and having first fitted the microscope to a due focal distance, I dropped, with the tip of a pencil, a quantity of water upon the object; when, in the course of some few seconds, I distinctly perceived a train of globules, involved in a filmy substance, to be ejaculated from within these minute bodies, and contorting itself from one side to the other during the time of action, which does not last above a second or two of time, and may be easily understood by a view of figs. 1. and 2. The drawings were taken from the pollen of the mallow. The several species of farina differ but little from each other in this particular, their action in general resembling that of an eolipile violently heated. I have since repeated this experiment upon almost every species of farina with the like success, particularly upon that of the pumpion, which afforded me a more than ordinary gratification, not only because the globules are larger than those of the farina of most flowers, and may be observed with the second magnifier, where I had the advantage of a large field, but also because I could plainly perceive by two or three lucid specks, which continually shifted their places during the time of action, an intestine commotion within the globules, and a stronger ejaculation of the emitted particles." He farther observed,

that some species of farina act with so much force, that, when two globules are contiguous, the action of the ejaculated substance in one will repel the other to the distance of six or seven times its diameter." Where the pollen was transparent, he could not perceive particles in the matter ejected, which appeared like a thin pellucid vapour; of which he cites the pollen of the Nasturtium as affording an instance. Mr. Needham made use of the reflecting microscope, and the above account will show that he obtained a correct view of his

object. His style is somewhat obscure, as he does not well distinguish between the pollen itself, which he calls globules, and the particles contained in, and ejected from, the pollen; but his meaning is sufficiently obvious to prevent any mistake respecting them. Fig. 1. represents

the pollen of the mallow ejecting the particles, as seen with his third magnifier; fig. 2. represents one grain of pollen in the act of ejection, as seen with his highest magnifier.

Mr. Needham asserts that the pollen should be fresh gathered; but this is not necessary, as Mr. Brown has proved. He also says that

the act of ejecting the particles continues only a few seconds.

This may be true with the pollen gathered in the summer months: but the pollen on which I made the experiment was taken from plants in the month of October, and the ac

tion did not begin till the pollen had been some time in water, and it continued for nearly an hour in many of the grains; others ejected the whole of their particles in less than a minute. The pollen of a hollyhock, which had been between the plates of mica in the slider of a microscope at least fifty years, emitted the particles very copiously, after immersion in water for four or five minutes. They were of different magnitudes, some being more than four times the size of others. When these particles were detached from each other, by stirring the drop of water, they continued to move about for some time, like the Animálcula infusòria: but when the grains of pollen had ceased to eject more particles, and the agitation from external causes ceased, I could never perceive any active motion of the particles, though I have repeated my observations frequently with different micro

scopes.

The first remarkable circumstance which takes place when the pollen is immersed in water is, sometimes, a change of form in the grains of pollen themselves. I was greatly surprised to see the pollen of the sweet pea change almost in

stantly from a cylindrical to a nearly globular form. Some of the grains which lay beyond the edge of the water being unchanged, gave me the opportunity of comparing them in these two forms. Frequently a transparent globule of considerable size, and sometimes two, are first protruded gradually through the coats of the pollen. Sometimes the

granules rush out rapidly in a mass, as represented in fig. 2.; at other times they flow out slowly in a winding train. The coats of the pollen sometimes burst in two places. The figures drawn by Mr. Needham very accurately represent the appearance of the pollen in action.

The year being far advanced when I began my observations, I was unable to extend them to many species of plants. I, however, carefully examined again and again the pollen of those plants that were accessible. Though I could never perceive any motion of the granules when they were clearly separated from the pollen, after the first ejection, it is not improbable that the particles within the pollen may possess greater activity in the summer months. I find it stated in p. 473. of your Magazine, that the Continental naturalists remark that the granules from the pollen of the same plant exhibit at one time a perceptible motion, and at another perfect immobility, under circumstances to all appearance

alike.

The accounts which have recently been published, of the seeds of certain species of mosses possessing spontaneous motion, and then sending forth roots, and becoming fixed vegetables, appear at first truly surprising. Mr. Ellis, the well known author of the work on Corallines, and a very accurate observer, was not unacquainted with this circumstance half a century ago, and has given a satisfactory solution of the phenomenon. He says the "minute seeds which evolve under water from fungi and mosses, and appear to have spontaneous motion, derive that motion from more minute animalcules in the water, which, by pecking at these seeds, moved them about in various directions, while the little animals were scarcely visible, till the food they had eaten discovered them." Other early microscopic observers were acquainted with the apparent metamorphosis of animalcules into vegetables.

In what has been advanced, it is not intended to deny the existence of active vegetable molecules, but to maintain that their existence is still problematical. That the tissues of all organic bodies may consist of molecules, and that these molecules may possess a moving power when detached from each other, seems accordant with many observations on the effects of macerating vegetable and animal substances in water, but