PLATE 5 
P. americanum 
A. —Columns of cells in a young, compact sorus. Uredospores arise by division of 
spore initial cells: p, peridial cell; i, intercalary cell; u, uredospore; s, stalk; b, 
basal cell. 
B. —Formation of stalked spores in a sorus in which space was provided by the 
early rupture of overlying tissues. Spore initial buds are arising from basal cells (at 
the left) so that the first spores will be borne on stalks. 
C. —Uredospores formed from budding basal cells. Nuclear division occurring in 
the bud from the second basal cell. 
P. agrirnoniae 
D. —Row of cells at margin of sorus, wedge-shaped intercalary cell below the peri¬ 
dial cell p. 
E. —Fully elongated peridial cells supported by intercalary cells beneath which are 
normal basal cells, not spores. 
F. —^Typical spore initial bud si, from basal cell (right); cell chain consisting of 
young uredospore, intercalary cell, basal cell, and ‘‘hyphal plate” cell; stalked spores. 
G. —Short stalk cells. Whether we find two spores or only one connected with the 
basal cell may depend on the way the cell is sectioned. 
P. hydrangeae 
H. —Four young uredospores, u, each supported by an intercalary cell. 
I. —Intercalary cell elongating somewhat. 
J. —Chains of cells in an aborted sorus. Intercalary cells beneath the peridium. 
K. —Cell chains at the margin of a normal young sorus; wedge-shaped intercalary 
cells degenerating. 
