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 w r ell 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 in 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 

 crystals 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 laver. 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 inorganic 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 in 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- 



