25 8 THE CELL-THEORY 



which the cell-membrane is deposited, subsequently expanding and 

 becoming separated from the nucleus, so as to form a complete cell ; 

 we need only say, that they have been long since set aside by the 

 common consent of all observers ; in Von Mohl's words (p. 59) : " The 

 whole of this account of the relation of the nucleus to the cell-mem- 

 brane is incorrect." The fact is, that in by far the greater proportion 

 of cases, new cell-development occurs by the division of the previous 

 endoplasts, and the growth or deposition round them and between 

 them, of fresh periplastic substance. The extent of this process of 

 division will be understood, if we remember that all observers now 

 agree in its being the method by which " cell-development " always 

 occurs, except in the embryo-sac of the Phanerogamia, the sporangia 

 of Lichens and of some Algae and Fungi. The so-called free cell- 

 development of the latter, however, by no means takes place in 

 accordance with Schleiden's views, but by the development of a cellulose 

 membrane (periplast) around a mass of nitrogenous substance (endo- 

 plast), which may or may not contain a nucleus ; subsequently 

 increasing, pari passu, with the periplast. And it is well worthy of 

 consideration, how far the process deserves any distinction, except in 

 degree, from ordinary cell-division, since the new endoplast is only 

 one portion of that of the parent cell, set aside for the purpose of 

 fresh development, while the rest undergoes no corresponding change. 

 However this may be, it may be regarded as quite certain that, leaving 

 out of view the immediate results of sexual reproduction, the whole 

 of the " cells," — the entirety of the periplasts and endoplasts — of 

 which a plant, whether it be a moss or an oak, are composed, never 

 are independent of one another, and never have been so, at any period 

 I of their existence ; but that, while the original endoplast of the 

 I embryo-cell, from which the plant sprung, has grown and divided into 

 all the endoplasts of the adult, the original periplast has grown at a 

 ' corresponding rate, and has formed one continuous and connected 

 envelope from the very first. The ground of his comparison, therefore, 

 is cut away from under Schwann's feet ; everj^ statement of Schleiden's 

 on which he relied turning out to be erroneous — as we shall see if we 

 turn to his original comparison of cartilage with a vegetable tissue 

 (pp. 9 — 17). Schwann, finding in cartilage cavities with more or less 

 distinct walls, in each of which lay a corpuscle, singularly resembling 

 the nucleus of the vegetable-cell ; finding also that the cell-wall was 

 close to this corpuscle in the younger parts, more distant from it in 

 the older (p. 24), naturally concluded that he had here, in the animal 

 world, an exact confirmation of Schleiden's supposed discoveries, and 

 of course gave to the corpuscle of cartilage the name of " cytoblast," 



