Aug. s» 19*3 
Anatomy of the Potato Plant 
231 
from the adjacent cortical cells in their smaller size, more regular arrange¬ 
ment, and lack of intercellular spaces. The tangential walls usually 
exceed in length the radial ones, though sometimes the cells are isodia- 
metric. Casparian strips are present, but the lignified area is not always 
distinctly noticeable. In fixed material the protoplasm is found adher¬ 
ing to these strips, but withdrawn from the tangential walls, and thus 
forms two slime strings. The cells of the endodermis contain some 
starch even when all other tissue is empty (PI. 31, A). This starch con¬ 
tent is in some plants the most constant criterion for the identification 
of the endodermis, since the Casparian strips are not always distinguish¬ 
able. 
Both cortex and pith are made up of irregularly spherical, rather large 
pplls interspersed with small, intercellular spaces. The pith often 
becomes hollow very early, but in certain varieties it remains almost 
intact until the plant is mature. 
The cells of the collenchyma of the potato plant are prosenchymatous 
in nature, and the walls are thickened in a highly characteristic manner. 
The deposition of thickening layers is restricted to the comers of the cell 
and to certain places in the radial walls (PI. 29, A, D), giving the lumen of 
the cell a more or less rounded outline in cross section. 
Both the epidermis and the subepidermal layer are made up of brick¬ 
shaped cells. Those of the epidermis are more regular and often isodia- 
metric; the tangential walls are slightly arched, the outer ones more than 
the inner. The outer wall has also a slightly developed cuticle. Here 
and there in epidermal cells anticlinal walls appear, suggesting late 
division among these cells. Some of the epidermal cells are specialized 
to form the guard cells of stomata. Beneath the stomata, chambers 
occur in the subepidermal cells (PI. 3 2, A). 
THE LEAF 
The leaf, with its petiole* may be considered as a lateral expansion of 
the stem, and its tissue as derived from and continuous with the latter. 
As seen in cross section (PI. 36, C), the vascular tissue of the petiole forms 
a semicircle, open toward the upper surface. The vascular bundles are 
surrounded on all sides by cortical tissue which merges into collenchyma 
just beneath the epidermis. Near the base of the leaf blade the outline 
of the cross section is semicircular; but toward the base the petiole 
gradually widens (PI. 43, C). This widening and consequent flattening 
causes the amount of cortical tissue to decrease on the convex side— 
that is, the lower side—and on the flatter side gradually to increase. The 
vascular tissue consists of distinct groups (PI. 43, C). The central group 
is relatively small; the two lateral groups, which are separated from the 
central one by more or less narrow gaps, are large. Isolated from these 
groups on each side there occur one or two small strands, which form the 
outer limi t of the semicircle and lie in the petiolar wings. As regards the 
