The Vegetable World: Being a History of Plants, with Their Botanical Descriptions and Peculiar Properties

found in some Roman tombs, dating from the second or third century of the Christian era, have not only germinated, but produced individual plants, which have in due course flowered and borne fruit. We must be on our guard against such prodigies as these. Although nature, as has been said, performs wonders, we must only believe in facts rigorously established, in order to avoid the mystifications and tricks which the malignity of the vulgar loves to play upon the infallibility of savants. e must not forget to speak of those wonderful seeds of wheat found in the tombs of ancient Egypt. It is now acknowledged

“Aeatsco that in this affair some one must have abused the confidence and credulity of the travellers. A variety of Wheat called Mummy Wheat is common, it is true, among farmers; but no authentic fact justifies its name. Though there is, as we have just seen, 8° great a difference in seeds as to the duration of their vitality, the difference is not less as regards the time necessary for their get mination. Some seeds, as Garden-cress, Poppy, and the cereals, germinate in a few days. Others, as those of the Peach, Almond-tree, Nut-tree, and Rose-tree, require one or even two years before they “come up.” This difference is owing partly to the size of the seeds, their hardness, and the woody nature of their integument; it is due also to the presence of a kernel round the seed.

There are some seeds which seem in such a hurry, so to speak, to develop themselves, that they even germinate in the fruit enclosing them. This very often happens among some sorts of Lemon-trees, and certain of the Cucumber family. ‘The embryo of the Mangrove, a tree inhabiting swamps, mouths of rivers, sea-beaches in the equinoctial regions of America, is developed inside the fruit, still hanging on the branches; and there can often be seen hanging from it a root more than a foot in length.

PHENOMENA OF LIFE IN PLANTS.

FEcUNDATION—GERMINATION.

The consideration we have given to the subject of the flower and fruit enables us now to enter on two great questions in vegetable physiology. Firstly, the influence of the stamens on in plants; secondly, germination. the pistil, or fecundation

FECUNDATION.

Of all the phenomena in the life of plants, there is none more interesting or more remarkable in itself than fecundation. When the existence of sexual differences in vegetables was first pro-pounded, the discovery produced general astonishment. If the most convincing proofs had not established it, if the commonest observation had not allowed every one to verify its reality, it would, certainly, have been classed among the most singular inventions that ever issued from a poet’s imagination. But the proofs were convineing. The demonstration of the existence of sexual organs in vegetables became a brilliant and unexpected fact, exhibiting a wonderful analogy between animals and plants; filling up in part the gulf which had hitherto existed between the two great classes of organic beings, yielding an inexhaustible fund of reflection and comparison to naturalists and thinking men. _. The ancients had very vague ideas on this subject. Yet we learn from Herodotus that, in his time, the Babylonians already distinguished two sorts of Date Palms; they sprinkled the pollen of one on the flower of the other in order to perfect the production of the fruit of that valuable tree.

Césalpin, an Italian philosopher, physician, and naturalist, who, — in the 16th century, was professor of medicine and botany at Pisa, remarked that certain sets of Mercurialisand Hemp remained sterile, while others were productive. He considered the first as the male sets and the second as the female. In the 17th century,

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THE VEGETABLE WORLD.

Nehemiah Grew, a learned English fellow of the Royal Society of London, who published in 1682 an Anatomy of Plants, above all Jacques Camerarius, a German botanist, born at Tubingen, showed the precise use of the two essential parts of the flower, and the part that each plays in producing the fecundation of germs. Ina letter now become celebrated, De sexu plantarum, published in 1694, Camerarius completely proved the great fact of the existence of the sexes in plants just as in animals. This discovery made an impression on the minds of naturalists; it was, in fact, one of the most striking victories which natural science had obtained.

After the labours of Camerarius, the existence of sexes in vegetables was generally admitted. Tournefort was incredulous, but Sebastien Vaillant, one of his most brilliant pupils, publicly professed in the Jardin des Plantes at Paris the theory of separate sexes in plants. In 1735 the celebrated Linnzus rendered it popular by basing on the sexual characteristics of vegetables his vast and admirable system of clas- nie sification, the importance of which we shall appreciate further on. The pollen having been recog-as the matter which fecun-dates the ovary, the next question was to discover in what manner the graius of pollen produced the fecundation of the vegetable germ. It was at first thought that the grains of pollen simply opened on the stigma, and that the granules which they contained, being absorbed by the stigma, went to form the embryo, or concurred in its formation. It was the most natural opinion to form&priori, yet observation has since proved that a much more Ba conte process takes place.: n 1823 Amici, an Italian natural ot nein Dimthic wile ducing te African Purslane-tree, perceived that the grains of pollen, far N 2

from opening, as was thought, on the stigma, in order to pour out the fecundating matter, changed by degrees into a sort of membranous tube, which he called the pollen-tubes, as represented in A, B, C, Fig. 272, which shows the successive stages through which the pollen passes when the pollen-tube is thrown out at the moment of fecundation. In 1827 the celebrated botanist, M. A. Brongniart, in his researches on this subject, perceived that the same fact recorded by Amici occurred in numerous plants; he observed also that the pollen-tubes generally penetrated more or less into the style. He instanced the Datura as one of those plants in which the action of the pollen on the stigma is very observable. ‘These tubular sacs,’ he says, “are for the most part already filled with granules, and easily distinguished from the tissue of the _ stigma by their brownish colour and opacity. I could not find a better comparison for one of these stigmata,”’ he adds, “than a pincushion entirely filled with pins stuck into it up to the head.”

Fig. 273 represents, according to the account of M. Brongniart, a vertical section of a stigma of Datura fecundated and furrowed with pollen tubes through all its thickness. Such is the appearance which the stigma of the Datura presents when strongly magnified.

Fig. 274 is intended to show the same arrangement in the same plant, but still more strongly magnified. The grains of pollen

and the pollen tube are here still more enlarged, the better to show the structure and passage of the tube through the substanceof stigma. In order to understand this curious organic peculiarity, Fig. 275

Fig. 274.—Conducting Tissue in Datura Magnified.

represents a similar stigma of the Datwra seen externally, and resembling, as M. Brongniart says, a pincushion full of pins. But such is the incessant progress of science, that in our days these early observations of M. A. Brongniart have been carried much further, and recent investigations show still more clearly the System of progression in the pollen-tube.

This tube, as M. Brongniart has shown, elongates itself by & most remarkable vegetative process, insinuating itself into the interstices of the cellular tissue, which has been designated from this cause the conducting tissue, and that doubtless by which it is

nourished. Occupying the centre of the style, this tube traverses its whole length, entering into the ovary, and is there brought in

Fig. 275.—Stigma of Datura covered with Pollen.

Fig. 276.—The Ovale. Fig. 277.—Section of the Ovule of _— Fig. Polygonum before Fecundation. contact with the ovules, penetrating by their micropylic perforations.

Fig. 279 is a section of the stigma, style, and ovary, and is intended to point out the long course followed by the pollen-tubes in penetrating from the stigma to the interior of the ovary, where each of them comes in contact with the ovules. One of these ovules is represented in Fig. 276, taken singly and magnified, to show this phenomenon more clearly. The ovule here represented is that of viola tricolor. The extremity of the pollen-tube, in contact with the summit of the ovule, proceeds to place itselfin still nearer connexion with one of the constituting cells of this nucleus, now excessively developed, in which state it bears the name of the embryo-sac, because there the embryo is fully developed and ready to burst. The same organ is represented, at the moment of fecundation, in Fig. 277. Here

Fig. 279.—Fecundation of the Ovule. an internal section of the ovule of the Polygonum is given, both before and after fecundation; a is the ovule before fecundation, 3, Fig. 278, the same organ after it. We see on the fecundated ovule sp, the commencement of the formation of the embryo-sac, at the terminating point of the pollen-tube. About the year 1837, two German botanists, MM. Schleiden and Horkel, announced that the vegetable embryo pre-exists as a

germ within the grain of pollen, and that it is formed of the end of the pollen-tube itself, while this extremity is lodged in the embryonic sac, whence it is driven back before it.

This theory, which reproduced, and seemed to take for granted, in the vegetable kingdom the celebrated hypothesis on the e-closure of germs put forth by Buffon for the animal kingdom, made much noise among the learned in Europe. It was supported by the personal observations of many of our best botanists; but it could not long resist the multiplied investigations that the importance of the subject called forth on all sides.:

M. Amici, Mohl, Uuger, and Hoffmeister soon demonstrated _ that, in fact, when the pollen tube had once reached the embryo-sac, it remained there, attached by its external wall, and that there its functions ended with its life; whilst a little vesicle plunged in the mucilaginous juice with which the embryo-sac is filled, absorbs by endosmose the fertilising elements which the pollen-tube has doubtless passed through its constituting membrane, and that this element is then developed so as to form the embryo. Schleiden’s theory of the pre-existence of vegetable germs received its final blow, when, in 1849, M. Tulasne, one of the ablest of French anatomists, published his magnificent studies on vege table embryogeny. M. Tulasne had always observed that the obtuse extremity of the pollen-tube was brought close to the membrane of the sac, strongly adhering there without causing any Pe! ceptible depression. At some distance from the point of contact, there was developed, on the membrane of the sac, a vesicle with a circular base, at first like a blister, which by cellular growth was soon transformed into the embryo. Fig. 280 represents the result of M. Tulasne’s observations, and the manner in which the extremity of the pollen-tube is introduced into the nucleus. F18 282 is an internal section of the same organ, showing the formation of the vesicle about to become the embryo, and Fig. 281 shows this vesicle now become a small globe of parenchymatous tissue, ® sort of rough sketch of the embryo, The embryo thus formed may acquire considerable development, and absorb for its own use all the soft matter contained in the embryo-sac; or it may be limited in size, and this soft matter, becoming a permanent and cellular