302 
STRUCTURE AND LIFE HISTORIES 
buoliana), the United States Department of Agriculture 
has issued quarantine regulations forbidding the impor- 
FIG. 222. White pine blister-rust. A, portion of diseased tree, show- 
ing pycnidial blisters broken open; from these blisters the disease spreads 
to neighboring currant or gooseberry bushes; B, early summer stage on 
under surface of a currant leaf; these spores repeat during the summer, 
at intervals of two weeks; C, early summer stage, much magnified; D, 
late summer and fall stage, on the under surface of a currant leaf; from 
this stage the disease spreads again to pine trees. (After Perley Spaulding, 
by courtesy of the U. S. Dept. of Agriculture.) 
tation of all five-leaved pines and all species and varieties 
of Ribes, except for experimental or scientific purposes by 
