Denniston—Growth and Organization of the Starch Grain. 667 
The plastid, in the formation of the starch grain, shows 
several points of resemblance to the plasma membrane in the 
formation of the cell wall. Both are plastic proteid bodies 
from which carbohydrates are formed. The carbohydrates in 
each case show a similar stratified structure, the starch grains 
being formed of laminae which are laid down upon the surface 
of the grain much as the cellulose layers are deposited in form¬ 
ing the cell wall. There is, however, probably no great signifi¬ 
cance to be attached to this similarity. 
THE STRUCTURE OF THE STARCH GRAIN AS INDICATED BY ITS 
STAINING. REACTIONS. 
Fritzsche (11, p. 129), in 1834, in the case of the potato 
starch grain, first noted the presence of concentric layers which 
completely surround what he called a spherical space. This 
space is usually located at one end of the grain. He believed 
the appearance of light and dark layers is caused by the vary¬ 
ing water content, and that the density of layers deposited by 
day is different from that deposited by night. The outside 
layer is of special density according to Fritzsche, due to 
its becoming infiltrated with a large amount of proteid sub¬ 
stance. 
Von Mohl (21, p. 45) believed as did Fritzsche, that starch 
grains consist of superimposed layers of varying density, but 
composed of the same substance. He found no cavity in the 
center in fresh grains, but noted that one is developed on dry¬ 
ing. FTageli (24, p, 18) also thought that the layers of the 
starch grain are due to differences in density as a result of 
varying water content. He believed that the layers are closed 
vesicles, and that they form, not one outside the other, but one 
inside the other. 
Schimper (36, p. 192) believed that the young starch grains 
are composed of a homogeneous dense substance. The grains 
increase in size, and a weakly refractive region de¬ 
velops in the middle. This is the hilum. The forma¬ 
tion of the hilum causes a reduction in the strain on the sur¬ 
rounding starch, with the result that a loose layer forms between 
two denser ones. 
41—S. & A. 
