8 Prof. H. Karsten on some Phenomena of 



nomena of the growth of cells, but also frequently the very form 

 of the Alga itself, even when this has been accounted a specific 

 character. 



The cultivation of Spirogyra has proved to me that this plant, 

 when liberally supplied with organic nitrogenous matter, gene- 

 rates new cells profusely, but that, if this nourishment be 

 withheld, growth is limited to the cell-wall. This observation 

 consequently shows that a deficiency of such organic nutritive 

 supply promotes the centripetal involution of the cell-wall of 

 Spirogyra, which in normal conditions of nutrition does not 

 happen. 



On the contrary, by a large supply of organic nitrogenous 

 material, the growth of the cell-wall, relatively to the formation 

 and evolution of new cells, remains in arrear. The cultivation 

 of such species of Spirogyra as S. Hornschuchii shows this. 

 The partition-walls (septa) of this plant, under normal conditions 

 of development, immediately after their origin produce circular 

 folds of a determinate size; and the tissue-cells (joint-cells) only 

 proceed to produce new cells, after the septiform circular folds 

 nave acquired their normal dimensions. (PI. I. fig. 4 a.) But 

 this same species, when richly supplied with nourishment in the 

 manner stated, presented in the same individual three, and 

 sometimes four, or even five partition-walls, without such circular 

 folds, and thus indicated that the thickening and further evolu- 

 tion of the cell-wall had been supplanted by an augmented de- 

 velopment of cells. 



The accelerated formation and development of new joint- cells was 

 accompanied by a considerable increase in the deposit of chloro- 

 phyll. The successive spiral coils of this substance, which are nor- 

 mally separated from one another by intervals of about twice their 

 width, approximated so closely frequently about the middle and at 

 the extremities of the cell as to touch, and sometimes to overlap, 

 each other at their edges, or, indeed, in their entire width ; the 

 spiral band being, relatively to the extension of the cell, dis- 

 proportionately elongated (figs. 7 & 8). 



In those instances where the layer of chlorophyll does not 

 acquire such an excess above its usual length, its increase will 

 nevertheless be indicated by a horizontal coil being substituted 

 in place of the normal oblique one, in the centre of the cell, over 

 the very delicate nucleus (fig. 4). This coil, at the commence- 

 ment of the development of new joint-cells, loses the concave, 

 furrowed character of its external surface, becomes pressed 

 against the wall of the cell and fixed in its central position, as it 

 appears, and as the further course of cell-development proves, 

 by the production of the daughter cells, which grow up from 

 the two opposite extremities of the cell, and extend themselves 



