302 



STRUCTURE AND LIFE HISTORIES 



hiioliana), the United States Department of Agriculture 

 has issued quarantine regulations forbidding the impor- 



FiG. 2 2 2. — 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 



