Denniston—Growth and Organization of the Starch Grain. 681 
We find thus that layers which appear single when mounted 
in water may be really double or perhaps even made up of a 
number of layers. The differentiation of the parts in such a 
case is not sufficient to enable one to make them optically dis¬ 
tinguishable as individual layers when the grain is mounted in 
water. That, none the less, considerable difference exists be¬ 
tween these parts is shown when the grain is stained. 
The regions of the dark lines 1 and 2, marking the surfaces 
of a, b and c, swell somewhat in the treatment with gentian vio¬ 
let and orange and stain a pale blue color. It is probable that 
these are thin spaces filled with watery solutions which are 
relatively slightly refractive. 
When gentian violet and orange are used after iodine, the 
spaces apparently open slightly and seem to contain some 
starch which is stained a pale blue. It is further noteworthy 
that although the layer c is not so refractive as b in water, it 
stains fully as darkly as the darker portion of b. The view i-s 
thus on the whole confirmed that the cause of the difference in 
appearance of the layers in grains mounted in water is due to 
their difference in density which in turn results from differ¬ 
ences in composition, the layers which contain the largest pro¬ 
portion of starch and the smallest proportion of water being 
the more highly refractive. 
A second grain (Fig. 43) from the same Ganna material 
was treated in the same manner as the grain just described. 
Drawings were made of identical portions of the outer layers 
of the grain as they appear with the different reagents: 
Fig. 43 A shows the grain mounted in water; B shows the 
gram treated with iodine, the drawing having been made be¬ 
fore the grain was completely darkened by the re¬ 
agent ; C shows the iodine partly washed out by the alcohol; 
D shows the layers stained by gentian violet and orange. The 
following table explains the appearance of the layers when 
treated with the different reagents: 
