r.36 FOREST COMMISSIONER'S REPORT. 



"The pine blister rust is a plant, living as a parasite in pines 

 for a part of the time and in currants and gooseberries for the 

 remainder. A seed (spore), which is carried by the wind, 

 perhaps, from a diseased currant bush in the fall to the bark 

 of a pine, sprouts there and sends its roots through the inner 

 bark of the tree in that region, and this growth of the roots of 

 the disease may continue for several years. The bark in this 

 region often becomes much thicker than elsewhere as a result, 

 or it may die, killing the tree before the disease shows on the 

 surface of the bark. Sooner or later, however, if the tree does 

 not die first, the rust grows out through the bark, and in the 

 spring forms masses of yellow seeds there, covered at first by a 

 whitish covering which soon breaks, and the seeds are blown 

 about. If any of them are blown on to currant or gooseberry 

 leaves, these seeds sprout and the roots grow all through the 

 leaves for a short time. After about two weeks these roots 

 grow out to the surface, and there produce seeds which can 

 be blown by the wind and which can produce the disease in 

 other currant or gooseberry leaves in the same way. This 

 process usually occurs about three times during the summer, 

 but as fall comes on the last set of seeds produced is different, 

 for these cannot spread the disease farther on currants, but only 

 on pines. The seed produced by the disease in the pines cannot 

 produce it in other pines, but only in currants and gooseberries, 

 while the first sets of seeds formed in these cannot start the 

 disease in pines, only the fall- formed seeds being able to grow 

 in pines. 



Explanation of Plate I. — A, A diseased white-pine tree with the 

 blisters broken open, spreading the disease to any currants or goose- 

 berries that may be in the vicinity; B, early summer stage on the lower 

 surface of a currant leaf, repeating on currant leaves during the rest 

 of the season, a new crop of spores appearing every two weeks ; C, early 

 summer stage much magnified; D, late summer and fall stage on the 

 lower surface of a currant leaf, spreading the disease back to neigh- 

 boring white pines. (Farmers' Bulletin, No. 742, U. S. Dept. of Agri- 

 culture.) 



