Nov., 1922] SPONSLER — STRUCTURE OF STARCH GRAIN 
473 
many problems involved in determining the physical structure, this phase 
will be described in considerable detail. 
The grain appears to have a layered structure somewhat analogous to 
that of an onion, that is, sphere inside of sphere. Strictly speaking, how- 
ever, the more truly spherical layers occur only near the center; the other 
layers are generally thicker on one side, making the shape of the larger 
grains eccentric. 
One group of investigators, working primarily with swollen grains, 
considered the grain as a sac composed of a different substance from the 
enclosed starch. The lamellar structure was more or less ignored. Leeu- 
wenhoek (5) and Raspail (10) were among the earlier members of this 
group, and Whymper (11) and Beijerinck (12) are among the present-day 
representatives. 
A smaller group report evidence sufficient to warrant the supposition 
that there is a series of concentric vesicles representing layers of the grain. 
Maschke (13) W. Baily (14), and Mme. Z. Gatin-Gruezewska (15) were 
advocates of this theory. 
By far the greater number of investigators have considered the layers 
as essential parts of the structure of the grain. That the layers differ in 
composition was held by Maschke (16), Nageli (17), Meyer (18), Kraemer 
(19), and Gatin-Gruezewska (15). That they differ physically, perhaps 
dense and less dense layers alternating, was favored by Fritsche (21), 
Miinter (22), Kabsch (23), Sachs (24), Strasburger (25), and de Vries (26). 
The possibihty of a crystalline structure of the grain was first brought 
out by Raspail (27) in 1825; but on account of its existence fully formed 
and free in plant cells, of its glossy round form, its insolubility in water, 
its color reaction with iodine, and its decolorization with alkali, he decided 
it could not be a crystal structure. 
Miinter (28) considered that he had proved the grains to be crystalline, 
although they could not be recovered in crystalline form, when he dis- 
covered that they would dissolve in sulphuric acid and that the solution 
would turn blue with iodine. 
Whatever these investigators may have had in mind concerning the 
structure of the crystal, it remained for Nageli (2) in 1858 to develop the 
first theory which was to hold a large place in the literature on the minute 
structure of the grain. He conceived the layers to be composed of invisible 
particles, and developed this theory along with his intussusception hypoth- 
esis of the growth of the starch grain in his monograph Die Starkekorner." 
It is a rather complex theory in that there are many assumptions concerning 
both the particles and the tensions and forces involved. In brief, the 
theory is as follows (2, pp. 332-377): The layers of the grain are built up 
of small particles of starch, the largest of which is invisible with the most 
powerful microscope, yet it contains over 9000 molecules of starch. These 
particles, which he later calls micellae (29), are surrounded by a water-shell 
