Dn'elopmaUf and Structure of the Vegetable Cell. 25 



aloDC : 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 joint-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 point, are 

 gradually removed more and more from the septum. These ex- 

 tremities, and at length the chlorophvll-bands in their whole 

 length, lose their spiral direction and become almost straight. 

 The number and size of their component vesicles appear at lirst 

 to augment, but subsequently they decrease, and in the end 

 completely vanish. The same happens also with the nucleus. 

 The other contents of the joint-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 whereiii 

 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 tranversc septum into two ; or, at least, this fission- 

 process IS in operation (I'l. VII. figs. 58-61 exhibit this condition 

 after the action of cndosmoiic floids). This process is rq)eated 

 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 less oblique direction, and are so closely ap- 

 proximated and compressed that it is difficult to follow their 



> vc-rtheless 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 iuteiior becuming simultaneously de- 

 prived of all secretion-matters, and es])ecially 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- 

 phyll is not caused by the change of the nutrient fiuids, although 



