Development, and Structure of the Vegetable Cell. 281 



normally developed and well-nourished cell, are for the most 

 part not perceptible externally, and which originate by the growth 

 of small yellowish-coloured vesicles, very similar to those of 

 chlorophyll in their earliest stage. In many cases also it may 

 be distinctly seen that a starch-corpuscle occupies the position 

 of a nucleus within mature chlorophyll-vesicles. 



Bary's idea that chlorophyll occurs in the external layer, and 

 starch more in the interior of the joint-cell, will not, therefore, 

 hold good. Indeed, in my researches on Vaucheria (Botan. 

 Zeitung, 1852), I showed that in that plant the starch was usually 

 to be found towards the exterior of the cells that contained 

 chlorophyll. The same obtains in CEdogonium, in those cells in 

 which new joint-cells have originated. The large, much-thick- 

 ened starch-corpuscles, when chlorophyll is not present with 

 them, are met with external to the cells which contain chloro- 

 phyll as well as delicately walled starch-vesicles. The explanation 

 of this relation is to be found in the successive development of 

 new endogenous cells within the joint-cell of the CEdogonium. 



As the phases of development of neighbouring joint-cells of 

 (Edogonium differ very much from each other, so also do the 

 joint-cells often present very different conditions in regard to 

 the distribution of the secretory materials contained within 

 them. 



The true nature of the functions of the nuclear cell (nucleus) 

 in relation to cell-formation in general, as well as to the multi- 

 plication of cells, in the case of (Edogonium, has not been 

 rightly understood. A cell-nucleus is frequently absent from 

 the cells of CEdogonium during the formation of new cells — 

 probably, indeed, more frequently absent than present; and 

 without doubt its existence, or rather its form, is dependent on 

 the conditions of nutrition and on the chemical composition of 

 the plasma. Besides, where the nucleus is present, it can be 

 shown that the origin of new cells, and still more the formation 

 of a septum, is quite independent of it. 



In those cells wherein a nucleus of the ordinary form exists 

 at the time of the formation of new cells, it is found to lie often 

 on the wall of the mother cell (fig. 28), often in the median line, 

 sometimes at its centre, and at others nearer to one end ; and, 

 in the course of the growth of the daughter cells, which do not 

 originate in contiguity with it, it becomes thrust to one side 

 along with the other contents, and pressed against the inner 

 wall of the mother cell. In this position it immediately begins 

 to undergo absorption — a process which seems to be frequently 

 preceded by a swelling-up of the nucleus. Mostly this act of 

 absorption is speedily completed ; and then only does a nucleus 

 make its appearance in each of the two new joint-cells, hitherto 



Ann. ^ Mag. N. Hist. Ser.3. Vol. xi'n. 19 



