THEORY OF THE CELLS. 205 



instead of forming, as they do, a new layer ; and why this new 

 layer does not constantly increase in thickness, instead of pro- 

 ducing a second layer around the crystal, and so on. In the 

 meantime we can do no more than express the fact in the form 

 of a law, that the coalescing molecules axe deposited rather along 

 the surface beside each other, than in the thickness upon one 

 another, and thus, as the breadth of the layer depends upon the 

 size of the crystal, so also the layer can attain only a certain 

 thickness, and beyond this, the molecules which are being de- 

 posited cannot coalesce with it, but must form a new layer. 



If we now assume that bodies capable of imbibition could 

 also crystallize, the two modes of junction of the molecules 

 should be shown also by them. Their structure should also 

 be laminated, at least there is no perceptible reason for 

 a difference in this particular, as the very fact of layers 

 being formed in common crystals shows that the molecules 

 need not be all joined together in the most exact manner 

 possible. The closest possible conjunction of the molecules 

 takes place only in the separate layers. In the common 

 crystals this occurs by apposition of the new molecules on 

 the surface of those present and coalescence with them. In 

 bodies capable of imbibition, a much closer union is possible, 

 because in them the new molecules may be deposited by intus- 

 susception between those already present. It is scarcely, 

 therefore, too bold an hypothesis to assume, that when bodies 

 capable of imbibition crystallize, their separate layers would 

 increase by intussusception; and that this does not happen in 

 ordinary crystals, simply because it is impossible. 



Let us then imagine a portion of the crystal to be formed : 

 new molecules continue to be deposited, but do not coalesce 

 with the portion of the crystal already formed; they unite with 

 one another only, and form a new layer, which, according to 

 analogy with the common crystals, may invest either the whole 

 or a part of the crystal. We will assume that it invests the 

 entire crystal. Now, although this layer be formed by the 

 deposition of new molecules between those already present in- 

 stead of by apposition, yet this does not involve any change in 

 the law, in obedience to which the deposition of the coalescing 

 molecules goes on more vigorously in two directions, that is, 

 along the surface, than it docs in the third direction corre- 



