WHITE-PINE BLISTER RUST. 23 



Recently Thayer (159) and Bunyard (8) have published results 

 of their studies of the cultivated red and white currants. They find 

 these currants to be of mixed and badly confused parentage, but con- 

 clude that certain varieties sprang from each of the three species, 

 Rihes mdgare, B. rubnim, and R. petraeum. Many varieties are still 

 to be assigned to the proper species ; hence, they are grouped in Table I 

 under the name R. vulgare, for convenience, as it is yet impossible 

 to assign all of them to any species. 



The gooseberries are well known to be in many cases a mixture 

 of Rihes reclinatum with several American species or even pure selec- 

 tions of American species. For convenience they are grouped under 

 the species name, R. reclinatum. 



Susceptibility of Ribes Species and Varieties to Cronartium ribicola. 



Estimates of the susceptibility of the various species and varieties 

 of Ribes have been made. (See Table I.) These are based on work 

 done in the greenhouse and on results of the experiments out of doors 

 on Block Island. These estimates have been made mostly by two 

 persons, so that they are believed to be quite reliable and accurate 

 by the standards chosen. The estimates for the inside experiments 

 were made entirel}^ independent of those out of doors. The two 

 agree surprisingly. They are based on the results of work covering 

 several years, but many of the species and varieties have been sub- 

 jected to infection but a single year. A few species will be noted 

 which have remained immune in our tests. But some of these 

 species are known to have become infected elsewhere. This is true 

 of Rihes alpinum which is reported to take this disease in Europe, 

 although it is entirely resistant in North America (35, 53). Rihes 

 innominatum has been well tested and took the disease only on newly 

 developed leaves. It is a very resistant species. Rihes sterilis, R. 

 tenue and R. villosum have not yet undergone satisfactory tests, so 

 that no conclusive statement concerning them can be made. 



The species of Ribes vary in susceptibility from the extremely 

 susceptible Rihes nigrum to the very resistant R. leptanthum. On 

 the former are produced the maximum number of uredinia and telia 

 of the largest size, while on the latter the minimum number is pro- 

 duced and these are poorly developed. Rihes alpinum, has been 

 entirely immune with us, although it takes the disease in Europe. 



The varieties of a cultivated species run fairly true to the species 

 as a whole. Some real variation among varieties is believed to depend 

 upon their mixed parentage. Many tests were necessarily made when 

 the plants were not at the most favorable stage of development for 

 the fungus to attack, and it is likely that further tests of aberrant' 

 varieties may bring most of them back into agreement with the species 

 to which thev belong. Of the varieties of the cultivated red currants 



