Development, and Structure of the Vegetable Cell. 277 



the lower sheath-like portion of the circularly torn membranous 

 wall, in consequence of the gradual expansion of the inferior 

 mass of the cell-contents. Bary regards the lower of the two 

 new and simultaneously produced cells as the parent of the 

 upper. 



The real process of cell-multiplication does not agree with 

 this description. The transverse cell-wall does not originate 

 only outside the enveloping membranous sheath, in accordance 

 with the prevailing opinion, by the inward growth, from the 

 surrounding wall of the elongated mother cell, of a fold-like or 

 lamelliform horizontal septum ultimately meeting at the centre, 

 but, on the contrary, it is present and complete before the rup- 

 ture of the membranous wall and the occurrence of the abrupt 

 elongation of the mother cell. 



The thickening, and not the formation of the transverse sep- 

 tum, follows after the changes described by Bary have taken 

 place in the mother cell when this escapes from the membranous 

 enveloping sheath, which until then encloses that portion of the 

 joint-cell in which the transverse septum arises, by the develop- 

 ment of daughter cells, in precisely the same way as the forma- 

 tion of cork-cells m Philodendron pertusum has already been 

 described. 



The existence of the transverse septum in the joint-cells which 

 are not yet elongated, and indeed in those in the upper end of 

 which the fold of the mother cell is already produced, is parti- 

 cularly easy of demonstration in the species of the genus CEdo- 

 gonium, as Hartig and others have indeed actually witnessed ; 

 but it is not so with respect to the mode of origin of the septum. 

 The great quantity of chlorophyll- and starch- corpuscles which 

 cover the inner surface of the cell- walls of these plants, when in 

 vigorous growth, renders it impossible to make out with any 

 certainty the development of new cells within these joint-cells. 



In my researches I employed plants of (Edogonium grande 

 which had been raised from spores in pure water, and many of 

 whose cells were scantily occupied by chlorophyll, so that the 

 changes which took place in the other contents could be more 

 clearly examined. 



In such plants it is possible to make out the true mode of 

 formation of the septum, which is thus effected : — two of the 

 many non-nucleated hyaline cells which occupy the interior of 

 the joint-cell acquire a greater size (PI. V. figs. 21, 26, & 28), 

 and by their growth press the others to one side against the 

 wall of the mother cell (which is coated with chlorophyll, starch, 

 &c.), and eventually come into contact and by their mutual ap- 

 position form the septum, often obliquely placed at first, and 

 completely fill up the cavity of the mother cell (figs. 27 & 29). 



