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- 
ducimg 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 are 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 
bemg 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 eoalescence 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 apart 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 does in the third direction corre- 
