Denniston—Growth and Organization of the Starch Grain. 679 
will slowly take on the characteristic bine color. In a short 
time the whole grain is colored uniformly a deep 1 , dark blue, 
but it is noticed that certain layers take the blue color more 
readily than others. The outer part of the refractive layer a 
is the first to show the iodine reaction, and in this it is follow¬ 
ed by the inner part of the same layer. These two parts of 
the layer a thus become clearly differentiated, and the inner 
part (a-", Fig. 42 B) takes the darker stain. 
Layer b takes on the blue color but slowly and remains for 
some time the lightest layer in the grain. It shows a marked 
contrast to the two darker layers a" and c. Layer c stains 
readily and in a short time becomes the most deeply stained 
layer in the grain. 
Although layers a and b are the first to show the effect of 
iodine, it appears to enter gradually around the peripheral 
portion of the grain until the whole grain is colored a dark 
blue. As a result of treating with iodine, the open region 1 
disappears and between a 11 and b a dark line appears. There 
is also a dark line between b and c. 
If we now wash out the iodine by drawing alcohol under the 
cover glass, we shall get the following results: When the wash¬ 
ing out is partially complete, it is seen to have been removed 
first of all at the periphery of the grain. The grain is kept 
constantly under observation, a drop of 95 per cent alcohol be¬ 
ing placed at one edge of the cover and drawn through by a 
piece of filter paper at the opposite side. The layer a of the 
unstained grain is now seen still more clearly to be composed of 
two layers, the outer one becomes colorless and the inner one a 
medium blue The crack-like region 1 } which appeared as a 
dark line in the grain stained with iodine, still appears as a 
dark line. This region is probably filled with an aqueous 
solution in the unstained grain, and closes up when iodine is 
applied. 
Layer b of the unstained grain, which colored but slightly 
in iodine, shows two regions when alcohol is applied, an outer 
pale blue region and an inner darker region. The dark line 2 
which is present at the inner border of b in water and in 
iodine, does not change in appearance with the alcohol. 
