Denniston—Growth and Organization of the Starch Grain. 695 
Ganna plants show the peripheral layer equally well, and at 
this time the grains were probably in a growing condition. 
As noted, starch grains from the rhizomes of Dieffenbachifi 
and the false bulbs of Phajus , which show the peripheral layer, 
were from plants which were presumably actively storing 
starch. 
The germinating grains of wheat, barley, rye and corn and 
the seeds of Coix show starch grains which have the orange- 
stained layer at the periphery, and this is clearly a corrosion 
layer. Thus we find this layer present both in starch grains 
which are growing and in those which are being used up, and 
the evidence is strong that it is a transition substance laid 
down as a continuous layer between the plastid and the starch 
strata. 
In the case of all the above starches, the orange-stained 
zone is not due simply to the washing in of the orange stain; 
this is the only region stained by the ordinary exposures to 
orange, and a much longer exposure does not stain the layers of 
starch adjacent to this peripheral layer. Further evidence that 
there is a differentiated peripheral layer is obtained by the 
careful use of the ordinary iodine staining, using a dilute solu¬ 
tion of iodine in water. A peripheral layer remains unstained 
while the inner layers are colored violet. 
The facts show clearly enough that there is a transition 
layer present between the plastid and the starch grain, and that 
this layer differs characteristically in its staining reactions 
from the starch of the inner layers. I am of the opinion also 
that this difference in staining reaction is evidence that the 
peripheral layer is chemically different from the layers be¬ 
neath. 
I have, in a preliminary paper (5), advanced the hypothesis 
that this peripheral layer is a viscid mother substance which 
becomes more and more concentrated by additions from with¬ 
out until layers of starch are laid down on its inner surface. 
Where the plastid surrounds the starch grain as a layer uni¬ 
form in thickness, we may suppose that the material in the 
peripheral layer is of the same density at every point, this den¬ 
sity increasing by the addition of fresh material till a layer 
