This memoir, which constitutes the first part of researches respecting the vegetable-cell, is dedicated to the author’s friend, Dr. F. Cohn. Its object is to afford a new doctrine and new views with respect to the primordial utricle, differing from those at present entertained. The author first proceeds to give an account of the primordial utricle, in accordance with which the principal part in the life of the cell is ascribed to that element which has been regarded as the essential, often the only completely closed, nitrogenous membrane of the plant-cell, and upon this subject the statements of some observers are communicated. A second section treats of the disposition of the contents of the vegetable-cell; these contents consist of the proper cell-fluid, which is always found in the interior, and of the external, peripheral, surrounding protoplasma (or more shortly, plasma), in which the granular portions of the cell-contents are always imbedded. A distinct lamination is apparent in this plasma, that is to say, it is constituted of an external, colourless layer applied to the cell-wall, and which never presents any granules, and termed by the author “the cutaneous layer,” and of an internal, frequently of a dense mucoid consistence and granular aspect, “the granular layer “of the author. When this granular layer is of some thickness the chlorophyll granules will be found lying in its outer portion, whilst the inner part will be seen to consist merely of a colourless, muco-granular substance, in which, it is true, many kinds of colourless, coarse, granular particles occur, but never chlorophyll-granules or amorphous chlorophyll. The parietal cytoblast is invariably lodged in the “granular layer,” and when this layer consists of two portions it is always found in the inner one. In cases where movement is observed in the cell, it always takes place at the boundary between the “granular layer” and the cellfluid. When the granular layer is thin, the whole of it moves together with the chlorophyll granules imbedded in it, but when it is divided into two portions, the movement involves only the inner layers beneath the chlorophyll-granules (Chara). The author supposes that the formative activity of the cell-contents is specially seated at the line of junction of the cell-fluid with the granular layer, and that it is the cause of the motion. In cases where the plasma does not constitute a continuous lining to the wall, it cannot, by means of reagents, be detached from the wall with a definite outline, but in the shape of a variously formed net-work of streaks of plasma. But when it constitutes a complete and uniform covering, it contracts in a continuous form under the action of the reagent, and under certain conditions assumes the false appearance of a membrane. Lastly, in cases where the plasma is divided, even in the cell, into two distinct layers, not only does the outer layer appear as a membrane, but the granular layer also presents a defined boundary. Whenever powerful re-agents are applied, and a rapid contraction thus induced, phenomena are always manifested, which necessarily lead to the assumption of the existence of a primordial utricle, although many different things have been included under that term. But when cells in which the primordial utricle is displayed in the most distinct form are treated with weak re-agents, although the same results are ultimately attained, the process, owing to the more gradual way in which it is effected, may be accurately observed, and it will thus be seen that it is not smooth membranes which are separated from each other, but a glutinous substance which is detached from a membrane to which it was adherent; the detachment frequently takes place only partially, and the connexion with the wall is maintained by isolated threads of plasma, which become more and more attenuated or are ruptured, until, at last, the outermost layer of the plasma, contracting, assumes the appearance of a membrane. This slow separation from the wall satisfactorily shows, in every case, that the internal coating of the cell is composed of a muco-glutinous, viscous substance, and that it is not, properly speaking, a membrane. The same considerations also confirm the author in his opinion that, when large cells are treated with slowly acting re-agents, the contents surrounded by the “cutaneous layer “often contract into two, or, more rarely, into several segments, whose connective portions becoming gradually attenuated are ultimately ruptured, and then isolated, though appearing to be bounded by an equally even and sharply-defined outline, as that of the whole contents previous to their division.

In the third section the author speaks of the cell-division in the Conferva, noting, in the first place, its mode of occurrence in Cladophora, and afterwards in Conferva, Spirogyra, and the Zygnemaceæ in general, in Œdogonium and the Palmellaceæ. Here also he endeavours to show that Mohl’s view of the process of division is incorrect, and that it is manifested in the way he describes only when Mohl’s mode of experimenting is closely followed. But when very dilute solutions are employed it is obvious that a delicate cellulose-septum exists even in the earliest stage of the division, and which was overlooked by Mohl. And further, that this delicate septum, is dissolved on the addition of acetic acid when the “cutaneous layer,” together with the “granular layer,” are detached from the proper cell-wall by weak re-agents (syrup); owing to which circumstance Mohl was unable to perceive this septum. The author recommends a dilute solution of chloride of zinc, in order to render the matter clear, from the circumstance that this agent first detaches the “cutaneous layer,” the septum still remaining, though it is afterwards also destroyed. It remained to inquire whether this delicate septum were a single or a double membrane, and observations on other algæ (Spirogyra), as well as in Cladophora, when the division was interrupted, show that this wall is double from the commencement, arising from a portion of the innermost cellulose-layer thrown out towards the interior. Having discussed the mode of division of the cell in Spirogyra, and the Zygnemaceæ in general, the author proceeds to notice the process in Œdogonium and the Palmellaceæ, and finds that the cells of Œdogonium differ from those above described in the circumstance that the walls of the secondary cells are not applied closely to that of the parent-cell, and, consequently, that a different mode of separation is manifested in this case. In Œdogonium also a substance is deposited in places between the parent-cell and the uppermost secondary cell, in the form of a ring of cellulose. In the gelatinous Algæ the wall of the secondary cell is also not in close opposition with the parent-cell, a substance being deposited between the two in all parts.

In the fourth section, the import of the “cutaneous layer,” as regards the cell, is shown. The subject of the author’s researches in this respect was afforded by Œdogonium, in which plant the multiplication of the contents does not commence until the elongation of the cell is completed. In this case the accumulation of the plasma may be observed, and the “cutaneous layer “be seen to constitute an incomplete streaky lining of the cell-wall. The result of these observations leads to the conclusion that the cutaneous layer of the plasma is the same substance as that of which the cell-wall is directly formed, and that the transformation of the “cutaneous layer” into the cell-wall takes place when the former has reached the highest stage of formation—that is to say—when it constitutes a complete parietal investment. The primordial utricle might, very readily, be taken for a membrane, but it is not a membrane distinct from the cell-wall, being merely its youngest cellulose layer, whose reaction with iodine depends upon the substances still adhering to it, since it is impossible that should be pure at this time. Usually it is only the outermost portion of the “cutaneous layer “which is intimately applied to the contiguous cell-wall, whilst the inner portion is gradually perfected, and eventually comes to be deposited in the same way. This just formed, youngest celllayer also constitutes the folds which advance so as to effect a complete constriction in the interior of the cell. But it occasionally also happens that the innermost part of the “cutaneous layer” becomes a young cell-wall, in which case the outer portion is left enclosed between layers of cell-wall. In this way is produced the so-termed “jelly” in the Palmellaceæ, and the cellulose ring in Œdogonium. All these formations are merely slight modifications of cellulose, which, on the addition of acids, is either rendered blue by iodine, or is converted into a soluble compound belonging to the amyloid series, and which is not coloured blue by sulphuric acid and iodine, Consequently, when the latter phenomenon is not manifested in a membrane, the absence of cellulose cannot absolutely be assumed.

The mode of division of the parent-cells of the pollen is discussed in the fifth section. After giving a historical summary of previous observations on the subject, the author states the results of his own researches in Allium Victorialis and Althœa rosea, in which he finds precisely the same conditions to obtain as exist in the Algœ. The formation of the septum is similar, except that in this case it becomes thickened before it is completely closed.

The sixth section is entitled “Nature of the cell-division in plants.” In this chapter the author shows that the capability possessed by the cell-wall of forming folds which are thrown out towards the interior is a general property of that tissue, and consequently that the act of division consists in the advancement of this plication till a complete constriction is effected.

In the seventh section it is shown that the free formation of cells consists in this : that the contents alone take part in the formation of the secondary cells, the membrane of the parent-cell having no share in it. But connected with this, various cases occur, which are more particularly specified by the author. He then adverts to the “swarm-spores,” which are said to possess only a primordial utricle, and is of opinion that the earlier limitation of these bodies is simply formed by the young cell-wall itself, which is unable to resist the powerful influence of re-agents, whilst at a later period, as the zoospore is more fully formed, it presents a stronger and firmer consistence. In a note, he remarks that the cilia of the zoospores are not motile organs, but for the purpose of attachment, and that the motion is induced in consequence of the perforation of the outer membrane, at which points a more active endosmosis takes place, as may be seen in the zoospores of Œdogonium, in which, when germinating, the opening through the outer membrane of the spore is always visible, from which the first commencement of the root proceeds.

The eighth section gives a resume of the foregoing observations, and in the ninth the author adds a few supplementary remarks upon the methods to be pursued in researches of this kind, and particularly upon the application of chemical re-agents under the microscope, and with respect to the period at which the division of the cells in the Cornfervœ may be best observed.