Development J and Structure of the Vegetable Cell. 421 



in figs. 36 & 38, only the central and less thickened or entirely 

 unthickened portion of it, inflating it at first in a globular form, 

 and subsequently occupying more or less completely the entire 

 space of the lower cell. 



In the normally developing septum the increase of volume of 

 the assimilating and growing cell-raembrane (fig. 40 a), which 

 manifests itself as a thickening, commences at the periphery, 

 and advances hence in the cylindrical part of the membrane to- 

 wards the ends of the two cells, in accordance with the growth 

 of their mother cell ; in the septum itself the advance is towards 

 its central point. 



If, by the stronger endosmotic distention of the neighbouring 

 uninjured cells, a greater pressure is exerted, soon after the 

 cutting of the cell, upon a septum of this kind which has not 

 long become liquefied, the septum is not grown through as 

 above described, but it is suddenly ruptured, and the contents 

 of the neighbouring and previously uninjured cells are pressed 

 out through the opening. 



A similar laceration of the new septal v»^all and escape of the 

 contents of a cell into the neighbouring cells, after the operation 

 of endosmotic fluids, takes place also in uninjured cells, and 

 appears to have furnished earlier investigators with support for 

 the idea of a septal formation by the growing in of a fold of the 

 parietal part of the membrane of the mother cell as far as its 

 middle line. 



Sometimes the downward-growing lower end of the upper cell 

 does not thrust the transverse wall before it in the median line, 

 but to one side, so that its lengthening extremity presents on 

 one side a very narrow, and on the opposite a much wider, an- 

 nular fold as the remnant of the original septal wall (figs. 37 

 &39a). 



I have more frequently observed instances where the down- 

 ward growing cell has not prolonged itself within the next dead 

 or cut cell beneath, but has thrust this entirely to one side, so 

 that the two cells appear in apposition, longitudinally, like two 

 wedges lying in opposite directions. 



Sometimes connected Conferva-filaments are met with in 

 which some single cell has become diseased and withered, and 

 then the immediately superior cell has grown in the form of a 

 root-cell into the cavity of the diseased cell, down to its bottom, 

 forming the next lower septum. This portion which has grown 

 down then begins to enlarge, until it entirely fills the cavity of the 

 diseased cell, and its lower extremity forms a perfectly normal 

 septum with the neighbouring cell. 



The very long joint-cells thus formed become, just as in the 

 case of the root-like cells produced from injured Conferva-cells, 



