210 THEORY OF THE CELLS. 
gated into a fibre ; and so with the other changes of form. Divi- 
sion of the cells can have no analogue in common crystals, 
because that which is once deposited is incapable of any further 
change. But this phenomenon may be made to accord with the 
representation of crystals capable of imbibition, just as well as 
the coalescence of numerous cells in the manner described at 
page 184 does. And if we ascribe to a layer of a crystal capa- 
ble of imbibition the power of producing chemical changes in 
organic substances, we can very well understand also the origin 
of secondary deposits on its inner surface as they occur im cells. 
For if, in accordance with the laws of crystallization, the lamina 
has become expanded into a vesicle, and its cavity has become 
filled by imbibition with a solution of organic substance, there 
may be materials formed by means of the converting influence 
of the lamina, which cannot any longer be held in solution. 
These may, then, either crystallize within the vesicle, as new 
erystals capable of imbibition under the form of cells; or if 
they are allied to the substance of the vesicle, they may so 
crystallize as to form part of the system of the vesicle itself: 
the latter may occur in two ways, the new matters may be 
applied to the increase of the vesicle, or they may form new 
layers on its inner surface from the same cause which led to 
the first formation of the vesicle itself as a layer. In the cells 
of plants these secondary deposits have a spiral arrangement. 
This is a very important fact, though the laws of crystallization 
do not seem to account for the absolute necessity of it. If, 
however, it could be mathematically proved from the laws of 
the crystallization of morganic bodies, that under the altered 
circumstances in which bodies capable of imbibition are placed, 
these deposits must be arranged in spiral forms, it might be 
asserted without hesitation that the plastic power of cells and 
the fundamental powers of crystals are identical. 
We come now, however, to some peculiarities in the plastic 
power of cells, to which we might, at first sight, scarcely expect 
to find anything analogous in crystals. The attractive power 
of the cells manifests a certain degree of election in its opera- 
tion ; it does not attract every substance present im the cyto- 
blastema, but only particular ones; and here a muscle-cell, 
there a fat-cell, is generated from the same fluid, the blood. 
Yet crystals afford us an example of a precisely similar pheno- 
