membranes in animals. Before any trace of cotyledons, while the embryo is very small, the Pleroma forms an axile cylindrical cord sheathed in two layers of cells, the periblem and dermatogen. Soon divisions appear in the dermatogen at the lower end of the embryo (near the suspensor), and the periblem increases to several layers on the sides of the embryo, but remains one-layered at both ends. These cell-divisions give rise to the root-cap and the primary bark. In the more developed embryo, where the cotyledons appear as two symmetrical projections, three membranes or layers of tissue (if the tissue be rendered transparent) are as clearly distinguishable in the cotyledons as in the axile portion of the embryo," &c. Professor Famintzin summarises his chief results as follows:-"In the earliest stages of the formation of the vegetable embryo, three morphologically distinct layers of tissue appear, which, during the complete development of the embryo, and most likely during the whole life of the plant, retain, with few rare exceptions (the embryonic vesicle for instance), their independence, and only certain. defined tissues are formed from them. In other words, they correspond exactly to the embryonic membranes of the animal kingdom." Gorup Besanez and Will made known that in the seeds of the vetch a ferment is contained which, on being abstracted by glycerine, can dissolve albuminous substances, such as fibrin, and render them capable of absorption. But while this was going on slowly but surely, Professor Morren of Liege rushed into the field, and, by his lucid and able work on "Vegetable Digestion," entirely removed the ground on which his opponents were standing by showing that the whole course of nature bore out the conclusions regarding digesting and absorbing plants. "In fact," he exclaims, "I see no difference between the alimentation of the plant and that of the animal; it seems to me necessary to characterise the process in plants by the same name. In other words, digestion has either no existence at all or it is common to all living beings." And again he says, "There is no ground for astonishment in all this, for, in my opinion, the facts observed among carnivorous plants are in perfect harmony with the general theory of the nutrition of plants;" and yet

again, "Digestion is common to all vegetables,-it seem s to be the necessary condition of assimilation."

These are bold statements, but they are no less true; and the whole of his able article on vegetable digestion is devoted to its proof. Not long ago in this Society we had an admirable digest of this work of Morren's, so that it would be superfluous for me to dwell at any length upon it. At the same time, as it is so well fitted to meet some of the most frequent scientific objections, I must cursorily recall some of the most salient points. Digestion is essentially a process of fermentation, whereby substances which would otherwise be insoluble are rendered soluble, and so fitted to to be taken into the system. In the animal economy we have various ferments playing an important part in the process of digestion. Thus the saliva contains ptyalin, which effects the change of starch into dextrin, and ultimately into glucose or grape-sugar. This is called the amylolytic action of saliva, and a small quantity of the ferment, under favourable circumstances, is capable of effecting the change in an almost indefinite amount of starch. Should this ferment fail in accomplishing the whole result desired, we have in the pancreatic fluid, which is poured into the intestine immediately below the hepatic secretion, one kind of ferment which acts as powerfully as ptyalin and for a similar object, so that any residual starch becomes transformed into grape-sugar. Now, in the vegetable kingdom we have a fine and familiar instance of a similar ferment in the germination of barley. Diastase is the name applied to it, but in its action it is identical with ptyalin and one of the ferments in the pancreatic juice, as it acts on the insoluble starch in the seeds, and by changing it ultimately, by means of hydration, into grape-sugar, secures its becoming available for the nutrition of the embryo. Now, diastase is also found in potatoes in the neighbourhood of its buds, where it effects a similar change. In connection with this, it is an important fact that chemists can establish no distinction between animal and vegetable diastase.

There is another ferment found in the mucus of the stomach and also in the succus entericus, which changes cane-sugar into grape-sugar; for though cane-sugar is

soluble, it is not absorbed nor assimilated by animals, and hence it must be digested. Now this ferment exists in the sugar-cane and beetroot; and when these plants are about to flower there is a great demand for nutritive material, the cane-sugar is accordingly transformed into glucose, and after the flowering it is found that the sugar has disappeared, part of it having been burned off in respiration, and the remainder having given rise to cellulose, as has been experimentally proved by Durin (" Comptes Rendus," July 3, 1876, p. 355).

The next digestive fluid which we shall consider is the gastric juice, which contains pepsin as its ferment, which changes the insoluble proteids into soluble peptones, and so renders them capable of being absorbed. And here again the pancreatic juice, by another ferment, which has been named trypsin, materially aids, and though there are differences between the effects of the two ferments, yet for our present purpose it will suffice us to regard them both as rendering soluble albuminous bodies which would otherwise have remained incapable of absorption. In the vegetable world we have a similar process; thus, in the grains we have stored up albuminoid materials under the form of gluten, legumin, and farina to supply the first necessities of the germinating period. These substances are insoluble in the cotyledons, but as the little plant is developed they are dissolved and are assimilated by the active protoplasm. We have already referred to the experiment of Gorup Besanez and Will, in which a ferment was extracted from the vetch which had the power of dissolving fibrin and of transforming it into peptones, thus resembling trypsin, for as this pancreatic ferment produces leucin and tyrosin, so in the case of legumin we have leucin and asparagin appearing; and not only so, but in the same Vicia sativa Will has shown the still greater resemblance to the pancreatic juice by obtaining another ferment which transforms starch into grape-sugar.*

*

* There is an interesting circumstance in connection with this double digestive agent in the case of yellow elastic tissue, or at least of elastin, which is its chemical basis. We know that this substance is insoluble by pepsin, and though Darwin declares that it is insoluble also in Drosera, yet in one instance I observed its solution in a leaf of Dionaa. On June 8, 1878, a small piece of ligamentum nucha was placed at 4 P. M. on a leaf of Dionaa. On

But we have yet to consider further changes effected in digestion by the bile and the pancreatic juice, which act on the fatty articles of food, the former slightly emulsifying them, and the latter both emulsifying and saponifying them, this last process being the splitting them up by means of hydration into glycerine and fatty acids. Oleaginous grains, when pounded in water, give a well-known emulsion, soon followed by glycerine and fatty acids; a similar action occurs during germination. Now we have accumulations of oils and fats stored up in the seeds of Cruciferæ, Papaveraceæ, Linaceæ, &c.; also in bulbs of onion, &c.*

This vegetable digestion is generally manifested in the depôts of nutriment which occur in seeds, tubercles, certain roots, bark, and pith. It occurs when vegetation begins, and the tissues are impregnated with water, &c.

Morren gives a table containing the proximate elements in the nutriment provided for the young plant, and he also gives one with the proximate elements in the nutriment provided for the young animal which afford a fine illustration of the similarity of composition; and if so, why should there not be a similarity of digestion ?

Next

June 10th, leaf was open, the fibre was wet, and the leaf again closed. day (11th), leaf was partially open, spikes slightly crossing X. June 13th, at noon, warm sunshine, distal half of leaf open, so that at the point the spikes are separate \, and the tissue is seen of a white colour. Proximal end is quite closed. It continued so till 17th. On June 19th it was quite closed throughout the whole extent. On opening it the piece of elastic tissue was found in it. It remained closed till July 1st, when, at 3.15 P.M., it was again examined, and the elastic tissue was found nearly dissolved. It was again closed, and was so on July 3, but, unfortunately, no further examination was made.

In the case of Drosera and Dionaea we know from Darwin's statements, and from our own observations, that fat is not digested by the secretions of these plants; but this circumstance, in their case, can be no disadvantage, for in the ordinary food of such plants, which consists of insects, there cannot be much danger of the fatty elements disturbing their digestion.

Hence, then, in all vegetables the embryo and buds during the first stages of germination digest the nutritive stores in their neighbourhood. When chlorophyll, however, is developed a new feature is manifested, for under the influence of light the plant becomes an instrument of reduction, and acts an intermediate part between the mineral and animal worlds, but the starch, oil, and albumen thus stored up are rendered soluble by digestion, and by absorption and assimilation made to contribute to the plant's own maintenance as well as to serve for the nourishment of animals. These views of Professor Morren are not peculiar to him, but express the opinions which the most eminent scientific observers now hold. I shall only refer to one, viz., Van Tieghem, whose ability and skill are everywhere acknowledged, and whose prolonged attention to this subject entitles him to speak with authority; and in his latest paper on the digestion of albumen* we find him thus expressing himself " All living things digest." He speaks of digestion being the act of a living being, by which it transforms by the aid of an active liquid produced by it, and renders soluble a substance formerly insoluble. It is in his view either external if the substance is outside the organism, and in this case is followed by absorption, or internal if the substance to be dissolved is in the cells of the body, and in such a case is not followed by absorption. "Infusoria and free vegetable aquatics, living exclusively on dissolved aliments, appear to be destitute of an external digestion; they are, nevertheless, like all the others, the seat of the internal digestive phenomena. It is by the free surface of the body that in certain regions the external digestion acts in their case, but similar digestive regions can be met with together or separately upon each of the three fundamental organs of vegetable apparatus-the roots, the twigs, and the leaves." One of the most interesting facts experimentally determined was that the digestion was in some cases completely effected by the cells of the albumen itself quite independently of the embryo, which in such a case performs simply the office of absorption. His experiments in proof were of two kinds. In the first case the albumen was carefully Comptes Rendus, tome 84, p. 578.