THE WHITE-PINE BLISTER RUST. 13 



of this development within the currant leaf. If it is abnormally 

 cold, progress is relatively slow. If the temperature is warm the 

 progress is rapid. With a favorable temperature, it requires 12 to 

 14 days for the parasite in its new home to produce a new crop of 

 spores. These always appear upon the lower surface of the currant 

 leaf in the form of tiny masses, hardly larger than a pinhead, of fine, 

 orange-yellow powder (PI. I, B and C) . Each of these masses is the 

 result of an infection of the leaf by a single Peridermium spore from 

 the pine. Naturally, the number of these occurring upon a leaf 

 depends entirely upon the number of Peridermium spores which 

 have stuck to that leaf; in fact, they vary from a single one up to 

 many hundreds on a single leaf. In many cases considerable areas 

 of the leaf surface may be completely covered with the powdery, 

 yellow spores, so plentiful has been the infection. These new 

 spores, very curiously, are quite distinct in appearance from those 

 on the pine from which they originated and are called uredospores. 

 Unlike the Peridermium spores of the pine, which can not reinfect 

 the pines, the uredospores of the currant leaf can reinfect currant 

 leaves. This stage is for this reason called a repeating stage. The 

 uredospores first produced from the Peridermium spores in turn are 

 blown about and fall upon the leaves of adjacent currant or goose- 

 berry bushes and there produce still another crop of uredospores. 

 This repetition may go on all the rest of the season, a new generation 

 of uredospores being produced every two weeks (fig. 4, 6 and c). 

 This is the time when the disease spreads most rapidly and to the 

 greatest distances. The progress made at this time, of course, 

 depends entirely upon the presence of some currant or gooseberry 

 bush near enough to the one originally infected so that spores will 

 be blown from the one to the other. In many parts of the country 

 currants and gooseberries are cultivated by nearly everybody who 

 has a garden, and in those sections there usually occur from one to 

 six or eight different species of wild currants and gooseberries in the 

 fields, pastures, and forests; so that a census of the currants and 

 gooseberries in a given locality often shows the best of opportunities 

 for the disease in this stage to spread rapidly and for long distances. 

 This stage of the disease is ordinarily found from June 1 until the 

 fall of the leaves. 



From the latter part of July until the fall of the leaves still another 

 form of fruiting body and of spores is produced upon the currant and 

 gooseberry leaves. This may appear upon the same spots which have 

 earlier produced the uredospores, but not always (fig, 4, &, c, and d). 

 The new form appears as groups of 3 to 10 or 12 short, stout threads, 

 not over a quarter of an inch in length and usually arranged in small 

 circles (PI. I, D, and fig. 4). Upon these threads are produced spores 

 of another distinct form. These are known as teliospores. These, 



