156 THE CULTIVATED EVERGREENS 



the bark of growth which is not more than three years old. 

 From these points it passes down into the larger branches or 

 even into the main trunk where it is able to grow in bark 

 thirty to thirty-five years of age. Here the fungus continues 

 to spread until, finally, girdling takes place with the resultant 

 death of all parts beyond the point affected. Infection is 

 brought about by spores which are blown by the wind from 

 leaves of currants and gooseberries in the summer and autumn. 

 One of the most troublesome characters of the disease is that 

 outwardly visible symptoms are not evident for approximately 

 two years after infection, and then only by careful observation 

 may one discern a slight swelling of the bark in the diseased 

 area. Later, usually about three years and six months after 

 the date of infection, the blisters from which the disease gets 

 its name push through the bark. These creamy-colored sacs 

 appear in the spring and soon break open and liberate millions 

 of yellow spores which may be carried as far as seven miles 

 by the wind. They are unable to reinfect pines, but, falling 

 upon leaves of currant or gooseberry, may produce the disease 

 there. In the early summer, upon the under side of such 

 leaves, yellow pustules appear which produce myriads of 

 another type of spore. These spores, which are produced 

 throughout the summer, are also unable to infect pines, but 

 serve to spread the disease to other currant or gooseberry 

 leaves. In the late summer small, brown, hair-like projections 

 arise from the same spots on the under surface of the leaves. 

 They may be so numerous as to give a brown felt-like ap- 

 pearance to the leaves. These hair-like projections consist of 

 masses of a third kind of spore which soon germinates where it 

 is, to produce yet a fourth type — the sporidia. Sporidia are un- 

 able to reinfect currants or gooseberries. Blown by wind, they 

 may infect pines within a radius of not more than 600 \'ards. 



