190 Prof. H. Karsten on the Formation, 



form independently of the neighbouring cell-membranes, but 

 identical or very similar phenomena exhibit themselves in 

 the membrane of the secondary cells, in the production of their 

 "secondary secretion-layers"; for were the layers of cell-mem- 

 brane known under this appellation only secretions on the inner 

 surface of a primordial sac, this last structure ought to be visible 

 so long as those laminae are in process of multiplication. 



Nevertheless no membrane is ever to be found between the 

 outer and inner so-called secretion-layers possessing the special 

 characters of the primordial sac. On the contrary, I am satisfied, 

 by repeated observations, that the membrane of the secondary 

 cell which is stained by iodine no longer retains its delicate 

 elastic consistence when the internal secretion-layers make their 

 appearance — a fact that favours the supposition that the sub- 

 stance of which the primordial sac is composed furnishes the 

 thickening layers by a change in the character of its activity. 



Restricting myself to preceding examples, I would recall to 

 mind the secondary cell of the pollen mother cell of Althaa : 

 no primordial sac can ever be discovered between it and the 

 primary cell, and nevertheless its laminar growth is continued 

 for a long time. 



There are even instances where such a transformation of the 

 substance of the membrane may without doubt be detected on 

 the coat of the tertiary cell (the cell-nucleus) whilst this mem- 

 brane is still far removed from the secondary cell-membrane. 



In PI. V. fig. 16 I have represented a cell such as is present 

 in the neighbourhood of the vascular bundles of many Palms, as 

 for example, Geonoma, Iriartea, Phoenix, &c. Within the cell- 

 nucleus of this almost cubical cell there is a collection of oxalate of 

 lime in minute crystalline druses, such as are not unfrequently 

 met with in cells. In these cells I found the membrane of the 

 cell-nucleus which lies close upon the secreted crystalline matter 

 transformed into cellulose — a condition which assuredly will 

 be often encountered. 



Moreover, in the globules of (Edogonium (fig. 50 h) all the 

 membranes of the entire system of cells exhibit a cellulose re- 

 action, though this is not the case in the youngest cells of this 

 same plant ; consequently a change of these latter into cellulose 

 must also have been efi"ected in this instance. 



The nature of the transformation which the several overlying 

 or nested cells of a cell-tissue progressively undergo depends 

 on the position which these cells occupy in the organism ; never- 

 theless the form which their membrane acquires during the 

 interchange of substance does not depend only on this trans- 

 formation, but in part also on the nature of their contents. 



For example, if the cell-contents are organized, and therefore 



