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 laminz 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 Althea: 
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 Pl. 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, Phenix, &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 erystalline matter 
transformed into cellulose—a condition which assnmedly will 
be often encountered. 
Moreover, in the globules of Gédogonium (fig. 50 b) 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 effected 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 
