224 
Journal of Agricultural Research 
Vol. XIV, No. 6 
flower color, of color and form of stem, of leaf and tuber that some vari¬ 
eties would hardly be recognized as members of the wild species. This 
is especially true of certain South American varieties recently introduced 
into this country. 
The aerial stem of the potato plant is herbaceous and erect when young; 
in age it becomes spreading. It is glabrous and three-cornered with the 
margins drawn out in the upper part to form ribs or wings which are 
especially prominent in young plants. Older specimens often lose these 
winglike borders; the subterranean part of the stem lacks them entirely. 
The latter is terete and differs further from the aerial portion in lack of 
chlorophyll and of dermal appendages. Stomata are present but rela¬ 
tively few in number. The leaves of this part of the stem are small and 
scalelike. In the axils of these, stolons arise. The tubers aie swellings 
of the ends of these stolons. 
The potato plant grown from tubers has no taproot; the roots are 
fine and fibrous, arising usually in groups of three just above certain 
nodes of the subterranean portion of the stem. These roots penetrate 
the soil to a depth of 3 or 4 feet and often extend horizontally 2 feet from 
the plant. Although the amount of root development is great, the 
relative weight as that compared with the aerial portion is very low. 
According to Hosaus (3), the proportions between root and stem in 
the potato is 1 to 44, while in other plants it is rarely less than 1 to 10. 
The leaves are arranged on the stem in a spiral with the divergence of 
■3^. The type of spiral is usually left, though numerous specimens with 
right spirals are found in plants raised both from seeds and from tubers. 
This is in agreement with a statement of De Vries (7), who found that 
the spiral of the eyes of the potato tuber may be either right or left, 
differing with the individual and with the variety. 
The petiole is semicircular in cross section. The adaxial side is slightly 
concave, the abaxial side strongly convex. The petiole becomes flattened 
toward the base, and there sheathes nearly one-third of the circum¬ 
ference of the stem. The winglike ribs or edges of the petiole are decur¬ 
rent on the stem unequally, one extending for one intemode, the other 
for two. The leaves are irregularly pinnate; the leaflets are more or less 
petioled, and between the larger leaflets supplementary leaflets occur. 
The number of these is not constant, but usually between two pairs of 
large leaflets one or two smaller pairs are found. The leaflets are oval 
in outline, with margins entire or sometimes serrate. There is great 
variation in the length of the petiole, the petiolules, and in the number 
of leaflets, a condition resulting in a loose or a crowded appearance. 
These characters are usually constant and characteristic of certain 
varieties. 
The venation of the leaves is of the netted type. From a strongly 
developed midrib lateral branches arise which anastomose freely, forming 
a dense reticulum. The course of the lateral veins is acrodromous, giving 
