AMERICAN 
JOURNAL OF BOTANY 
Vol. IX November, 1922 No. 9 
THE STRUCTURE OF THE STARCH GRAIN 
O. L. Sponsler 
(Received for publication January 23, 1922) 
Although starch is one of the most common and most widely distributed, 
as well as one of the most widely used, of organic substances, there is amaz- 
ingly little known about it. During the past two centuries fully five 
hundred investigators have worked with starch, and yet there are only a 
few points which seem to be at all well established. In 1836, Poggendorff 
(i), in his review of the work done on starch, wrote that "no substance has 
been investigated more and is still less known"; Carl Nageli (2) in 1858, 
Arthur Meyer (3) in 1895, and E. T. Reichert (4) in 1913, in their large 
monographs express a similar view; and a reviewer of 1921 would very 
probably arrive at the same conclusion. 
One commonly thinks of starch as a product of corn, wheat, and other 
cereals; or of the potato tuber, the cassava root, or the stem of the sago 
palm; and recognizes it as a product of plant life, and as the principal 
form in which food is stored. 
Commercially it is separated by grinding the plant tissues in which it 
is stored and allowing it to settle out from a water mixture. When washed 
and dried the white powdery mass is the starch of commerce. 
Under the microscope this powder is seen to consist of minute, trans- 
parent, glossy beads, varying in size from i/io of a millimeter down to the 
limit of visibility, that is, about 4/10,000 of a miUimeter in diameter. They 
vary also in shape, although the general tendency is towards a rounded, 
approximately spherical form. On close examination in water they appear 
to consist of a series of more or less concentric layers, or lamellae. In 
polarized light a dark cross appears in each grain. If, however, the grains 
are made to swell by treating them with hot water, or with certain chemicals, 
the dark cross disappears. 
The natural whole grains seem to be insoluble in cold water; but if 
treated with hot water or if the individual grains are crushed, they swell 
and appear to go partly into solution. The air-dried grains usually contain 
a high percentage of moisture, often up to 20 percent. 
[The Journal for October (9: 415-469) was issued October 20, 1922.] 
