Denniston—Growth and Organization of the Starch Grain. 683 
appear as a dark line except in water, and in its place there ap¬ 
pears a layer which is pale bine in iodine and in gentian violet 
and which probably contains very little starch material. This 
layer appears to swell when iodine or alcohol is applied, due no 
doubt to the contraction of adjacent layers. 
Layer c is less refractive in water than either a or h and 
probably contains less starch material. In iodine and also in 
gentian violet it contracts considerably and takes a pale color 
with both these reagents. 
From the study of grains such as the above it is plain that 
the ordinary conception, that the visible elements of the 
grain consist of denser layers of starch alternating with more 
watery layers, must be extended to include the appearance of 
sharp lines marking the boundaries of the highly refractive 
layers and also spaces which are practically open crevices be¬ 
tween the layers and which may become wider or narrower 
with the contraction or expansion of the denser layers or of 
the entire grain. 
The grain of Figure 42 shows the existence of crevices most 
clearly. Such a crevice appears conspicuously between a and 
b when the grain is mounted in water. It closes up and ap¬ 
pears as a dark line when the grain is mounted in iodine solu¬ 
tion, and as a narrow light blue layer in gentian violet. Sim¬ 
ilar crevices exist at 2 in the same grain and at 1 and 2 in the 
grain of Figure 43, although the latter are narrower. Such crev¬ 
ices are most sharply distinguished from the starch layers by 
the readiness with which they change their width on the appli¬ 
cation of reagents toi the grain. Their width is apparently 
entirely determined by the swelling power of the adjacent 
layers, and it is to be noted that the inner layers of the grain 
appear to be less dense than the posterior layers; they contract 
noticeably when alcohol or iodine is applied. 
The refractive layers also vary in thickness and density. The 
thicker layers do not all color with the same intensity with 
iodine or with gentian violet. It is also clear that those layers 
which take the deepest color are in general the densest layers. 
42—S. & A. 
