132 Prof. H. Karsten on the Vegetable Cell, 



The other extreme of this fold-formation is represented in 

 fie 82 from a plant which had lain for some tune ui water con- 

 taining carbonic acid; hence the thickening of the primary 

 membrane of its joint-cells. The endogenous cells were here 

 in complete apposition, forming a perfect septum. Squeezed in 

 between them is a fold of the wall of the mother cell, which in 

 this case did not grow regularly from the whole periphery into 

 the cavity of the cell between the daughter cells, but only pro- 

 jected far into it in a part of its extent, whilst another portion 

 "of the circumference remained unaltered. 



At this part, which was not affected by the folding, the 

 chlorophyll-sacs, which were elongated simultaneously with the 

 formation of the fold, are seen bent and crooked, as if they had 

 been acted upon by a mechanical constriction. Others are 

 separated into fragments, as in the normal formation of a 

 septum. A joint-cell of this kind, seen from the side on which 

 the fold is perfect, may readily be regarded as completely 

 divided; and this illusion may be increased by the position of 

 the new cell-nuclei, when, as in the case figured, they are large 

 and filled with granular mucilaginous matter, situated in each of 

 the new cells, not in the middle, as in the examples described at 

 p. 125, but close to the new septum, and when seen in a parti- 

 cular direction appear like a cell-nucleus cut through by the 

 fold. 



It is rarely that, as in Clndophora, these folds appear to pro- 

 ject freely to a greater or less distance into the cell-cavity; 

 nevertheless I have repeatedly observed this on apparently per- 

 fectly healthy plants, especially of S. orihospira. 



In diseased and dying plants, the joint-cells of which are 

 often disproportionately short, the folds of the membrane are 

 usually more developed, so that it would almost appear that 

 the development of the two parts stands in a certain mutual 

 relation. 



These folds may be most readily seen when Spirogyrce are 

 allowed to lie for a long time in water containing carbonic acid 

 until all the endogenous cells of the joint-cells are destroyed. 

 By the action of dilute endosmotic solutions, the membrane of 

 the secondary cell then readily retracts itself, together with its 

 still adherent chlorophyll-sacs, from the folded primary cell- 

 membrane, producing appearances which would certainly appear 

 well fitted to confirm the constriction-theory, if we were not 

 undeceived by developmental history and analogy. 



These folds, which occur in all degrees of breadth and differ- 

 ence of form, are, however, not destined to effect a-niultiplica- 

 tion of the joint-cells by the growing together of their central 

 margin, any more than those of Cladophora, many of which 



