Mar. is, 1924 
Studies on the Potato Tuber 
825 
It dissolves easily in hot alcohol, slightly in benzol, cold alcohol, and 
'ether. Solanin is found in large quantities in the young tuber; in the 
mature tuber only in the region of the buds. Upon renewal of growth it 
begins to accumulate in larger quantities, and as it gradually disappears 
from the base of the tuber it becomes more evident in the shoot. The 
distribution and formation of solanin suggest that it is important in the 
metabolism of the growing plant. If germination is held back in the 
spring, solanin may accumulate in such quantities in the tuber, as von 
Brehmer has shown, as to be poisonous to man. 
Tannin. —One of the most conspicuous and interesting forms of cell 
inclusions is tannin. In the growing tip it occurs in two forms, as fine 
granules, notably in the older periderm cells, and in the form of spherical 
vesicles in the neighborhood of the buds (PI. 8, A, C, and colored PI. i, 
C). The vesicles occur abundantly in the germinating tuber. They 
color blue with iron salts and black with osmic acid, and of themselves 
may be brown or blue. Their content is either a fine granular substance 
or a homogeneous brown fluid. The larger vesicles, which sometimes 
fill the entire cell, often contain a number of small globules within them. 
Sometimes the vesicles are of a lighter color, or even colorless; some¬ 
times they form mere refractive drops. Sorauer (17), who made an 
extensive study of the nature and distribution of these bodies, observed 
that the white tubers contained mostly brown vesicles and that in 
colored varieties a mixture of brown and blue vesicles was found. 
STRUCTURE OF THE STOLON WITH SPECIAL REFERENCE TO FOOD 
CONDUCTION 
In the structure of the mature stolon the epidermis, and the vascular 
tissue merit special consideration. In the tuber, as we have seen, the 
epidermis is replaced by a many-layered periderm, while in the stolon 
the epidermis is retained, but its outer walls and cover hairs become 
lignified. In the development of the vascular tissue strength has been 
sacrificed for efficiency in conduction. The xylem forms a continuous 
ring, composed mostly of large porous vessels. The area occupied by 
the outer and inner phloem is relatively greater than that in the stem. 
Sieve tubes are numerous and of a large diameter. The sieve tubes of 
the secondary phloem are especially large and measure as much as 20 
microns in cross section. 
An average-sized stolon bearing a medium-sized tuber had the following 
tissue areas (fig. 6 and Table I): 
Tabus I .—Relative areas occupied by the different tissues of the cross section of a 
mature stolon. 
Stolon tissues measured. 
Area. 
Per cent of 
total. 
Cmcc cp> r*tintitil nrpfl nf stolon ... 
Sq. mm. 
2 . I3O 
.277 
.239 
• 174 
•350 
1. 090 
IOO. O 
l 
OVnss votional area of outer tYhloem ... 
sectional area of inner ohloeni ... 
V 24. 2 
Pfnoc certional area of xvlem . 
8.2 
Arw? sectional area of r»itli. 
16.3 
SI* 3 
Cmcc oectional area of cortex. 
85606—24 - 2 
