Development, and Structure of the Vegetable Cell. 25 
alone : they appear to require for their nutrition soluble organic 
compounds. 
If a Spirogyra be allowed to grow for a considerable time in 
pure water, free from organic compounds and from dead or dying 
organisms, and its jomt-cells be measured from time to time, 
these are found to undergo an unusual increase in length, and 
sometimes a certain augmentation also in width. At the same 
time the circular bands of chlorophyll diverge and become more 
oblique ; their extremities, which were situated in the vicinity of 
the septum, or even bent inwards towards its central poit, are 
gradually removed more and more from the septum. These ex- 
tremities, and at length the chlorophyll-bands in their whole 
length, lose their spiral direction and become almost straight. 
The number and size of their component vesicles appear at first 
to augment, but subsequently they decrease, and in the end 
completely vanish. The same happens also with the nucleus. 
The other contents of the joimt-cells grow more transparent and 
hyaline. 
But if a small quantity of the mucilaginous juices of the same 
species or of some other Conferva be added to the water wherein 
the starved Spirogyra is placed, a new vital energy manifests 
itself, and many or all the joints are found in a short time di- 
vided by a tranverse septum into two; or, at least, this fission- 
process 1s in operation (PI. VII. figs. 58-61 exhibit this condition 
after the action of endosmotic fluids). This process is repeated 
again and again, when the necessary supply of nitrogenous organic 
matter is afforded. The spiral bands of chlorophyll in the joint- 
cells also pursue a Jess oblique direction, and are so closely ap- 
proximated and compressed that it is difficult to follow their 
course. 
Nevertheless it would seem that these plants can be sub- 
mitted to starving only to a certain degree, and afterwards be 
capable of renewing the act of cell-formation—a process which is 
evidently completely arrested when azotized matters are absent 
from the water in which they grow. Under this latter condition 
no growth proceeds, save in the membranes of the already ex- 
isting joint-cells, their interior becoming simultaneously de- 
prived of all secretion-matters, and especially of such as are 
nitrogenous in character. The chlorophyll-bands, which are 
stretched out quite straight when all the endogenous cells are 
absorbed, take on a more and more crooked direction between 
the inner surface of the mother cell and the outer wall of the 
daughter cells in proportion as the latter, departing from an 
ellipsoidal, approximate to a spherical figure. 
. An increase or a decrease in the number of bands of chloro- 
phyllis not caused by the change of the nutrient fluids, although 
