824 
Journal of Agricultural Research 
Vol. XXVII, No. XI 
observed in which each component has a hilum and striations of the nature 
found in the large individual grains. 
Nitrogenous substances in various forms, as constituents of the proto¬ 
plasm or dissolved in the cell sap, are found most abundantly in the cam¬ 
bium, the phellogen, and in the region of the buds; also in the form of 
crystals in the peripheral cells of the cortex. The protein crystals appear 
very early and can be found even in the tuber primordium. They increase 
rapidly in number and size as the tuber enlarges, so that in the mature 
tuber more than one may be observed in a cell. The crystals are always 
cubical in form, but their size varies greatly. The larger and more typical 
crystals have a diameter of 12 microns (PI. 1, C). Upon germination the 
cleavage products of the protein crystals form, according to Sorauer, the 
first food for the developing buds. 
A small amount of fat is found in the periderm cells and in the peripheral 
cortex. Inulin is absent, but organic acids—citric, succinic—are present, 
lending the tuber an acid flavor which is apparent even without analysis. 
Sugar is not found in the mature tuber, but becomes abundant upon re¬ 
newal of growth. 
Crystals. —Besides the typical protein crystals described above, two 
other types are commonly observed—calcium oxalate, in the form of 
crystal sand, found in special cells and observed first in the cortex of the 
young stolon. In the older tuber those cells often occur in vertical rows. 
The crystal sand consists chiefly of small crystals of calcium oxalate in 
the form of octahedrons and their derivatives. Together with the cal¬ 
cium oxalate there is always a protein matrix which remains after the 
crystals have been dissolved by acids. The crystal-bearing cells increase 
in number and appear not only in the cortex but also in the pith. In 
the mature tuber they disappear, but become evident again in large 
numbers in the region of the buds in the germinating tuber. In the 
peripheral cortical cells there are found occasionally crystals of basic cal¬ 
cium phosphate. These form four-sized prisms with pointed ends; 
however, they appear rarely in pure crystal form and often contain col¬ 
oring matter. In time of their appearance the phosphate crystals are 
later than calcium oxalate. Sorauer considers calcium oxalate crystals 
a decomposition product of the carbohydrates, and the phosphate crys¬ 
tals a residue of protein metabolism. 
Soi/ANiN. —When a section through an eye is treated with alcoholic 
phloroglucinol, it will be observed that the region of the buds stains a 
deep orange. The color is most intense in the epidermis and in the 
parenchymatous cells inside the vascular cylinder. Similarly, when a 
section is treated with concentrated sulphuric acid or ammonium vana¬ 
date with sulphuric acid (1 part of ammonium vanadate is dissolved in 
1,000 parts of sulphuric acid, prepared by mixing 98 parts of sulphuric 
acid with 36 parts of water), the following color reaction is observed: 
Yellow, red-yellow, brown-red, dark red, violet, fading out. According 
to von Brehmer (2), who studied the distribution and migration of solanin 
in the potato, there is only one color change, from yellow-red to violet; 
all other colors merely indicate different concentrations of solanitn. Von 
Brehmer found in his studies that solanin can not be extracted with water 
and is not held in combination by acids, and suggested that it is held in 
solution by colloidal proteins. Upon germination the solanin content 
diminishes in the peripheral cortex and becomes evident in the elongat¬ 
ing shoot. Solanin is a glucoside which upon hydrolysis gives solanindin, 
galactose, rhamnose, and, as an intermediate product, a complex sugar. 
