26o THE CELL-THEORY 



Let us compare, then, some young vegetable tissue, say that of the 

 base of a Sphagnum leaf (fig. 2, A), which is in many respects very 

 convenient for examination, with that of young cartilage (fig. 3, A) ; 

 the identity of structure is such, that it would be difficult, without the 

 aid of chemical re-agents, to distinguish one from the other : in each, 

 we see highly nitrogenous, more or less vesicular endoplasts imbedded 

 in a homogeneous transparent substance, whose cavities they wholly 

 fill. If we trace the further development, we find that in the Sphagnum 

 leaf the endoplasts and their cavities rapidly increase in size (fig. 2, B), 

 the former becoming, in certain localities of the leaf, regular primordial 

 utricles without any nucleus, and growing in exact proportion to the 

 cavities in the periplast {b), while in other directions, having attained 

 a certain size they cease to grow, and rapidly disappear, leaving the 

 periplastic cavity empty («). In cartilage precisely the same thing 

 occurs. The endoplasts increase in size for awhile, and then stop, 

 while the periplastic cavities continue to increase, and thus we have 

 eventually a cartilage-cavity with its corpuscle. In old cartilage the 

 latter frequently disappears, or is converted into fat. We have here 

 purposely selected, in both the animal and the plant, simple cases, in 

 which the endoplast becomes a primordial utricle, without any nucleus. 

 Had we selected the cambium of a phoenogamous plant, it would have 

 been merely necessary to add that, as the endoplast grew, a nucleus 

 appeared in its interior ; and in ossifying cartilage, near the ossifying 

 surface, we have repeatedly seen endoplasts such as those described 

 above, some of which contained definite " nuclei," while those in their 

 immediate neighbourhood possessed none. 



In the case of cartilage, then (and it is a conclusion at which Leidy 



and Remak have already arrived), we hold it to be proved that the 



>5j ■ corpuscle does not correspond with the nucleus of the plant as Schwann 



? supposed, but with the primordial utricle, contents and nucleus ; or, in 



other words, that the " nucleus " of cartilage is the equivalent of the 



r " primordial utricle " of the plant — that they are both endoplasts. It 



{ follows, hence, that the chondrin-wall of the cartilage is the homologue 



of the cellulose wall of the plant, and that they both represent the 



periplastic element. The phenomena of growth and multiplication 



exhibited by these corresponding elements are perfectly similar. The 



process of cell-division, as it is called, is identical in each case. In 



the plant, the primordial utricles divide, separate, and the cellulose 



substance grows in between the two. In young cartilage the same 



thing occurs, the corpuscles divide, separate, and the chondrin substance 



eventually forms a wall of separation between the two. There is 



neither endogenous development nor new formation in either case. 



