THE GROWTH OF STARCH-GRAINS 37 



shown that, contrary to Nageli's assumption, the outer layers are not always 

 denser than the inner. Similarly, the internal strains observed in starch-grains 

 could easily be produced by apposition combined with subsequent internal 

 changes, and no arguments as to the mode of growth can be deduced from 

 the supposed molecular structure, which is itself a mere hypothetical abstraction. 



The formation and growth of the starch-grain is more closely connected 

 with the vital activity than is the deposition of proteids or of calcium oxalate 

 by crystallization. If, however, the causes are discovered which lead to the 

 assumption of a definite shape by the crystals of calcium oxalate in a particular 

 cell, we should be able to deduce the conditions existing in the cell during 

 their formation. In the absence of any stimulus to crystallization, a super- 

 saturated solution may be produced, a drop of which will crystallize centripetally 

 around a suitable particle to form a sphaerocrystal \ The formation of such 

 supersaturated droplets is a common phenomenon within the cell, and they may 

 either crystallize individually or by aggregation 2 . 



1 Hansen, I.e., p. 120; Meyer, I.e., pp. 151, 192. Cf. also Biitschli, Unters. ii. Structuren, 

 1898, pp. 204, 300. 



2 Cf. Ostwald, Lehrb. d. allgem. Chem., 2. Anfl., 1891, Bd. I, p. 1041, and Butschli, I.e. 



