76 BULLETIN 957, U. S. DEPx\ETMENT OF AGRICULTURE. 



It has been possible to learn a little more concerning resistant 

 species and varieties of Ribes, Rihes alpinum is found to be immune 

 in America, although it is stated that it takes the blister rust in 

 Europe. There does not appear to be any resistant species which 

 will take the place of the cu].tivated R. nigrum (the black currant), 

 or of R. odoratum (aureum) (the flowering currant). Among the 

 cultivated red currants the varieties Franco-German, London, 

 Rivers, and Holland have shown themselves very resistant. In 

 generally infected areas these may prove of value to replace the 

 more susceptible varieties. 



In the outbreak area at Eattery Point, Me., one of the oldest in 

 North America, the infected pines are thickly crowded together and 

 mostly range in height from 15 feet upward. The lower branches 

 are being suppressed and are dying rapidly from overcrowding. 

 Experience has shown that trees and branches attacked by the 

 blister rust are weaker than healthy ones and are more apt to die 

 from drought and suppression. Posey and Gravatt" find that this 

 natural suppression of lower branches at Kittery Point has resulted 

 in the killing of many entire branches bearing blister-rust cankers 

 well out from the trunk of the tree. In such cases the disease in the 

 dead branches is killed also. They find that about 15 per cent of the 

 trees originally infected have thus recovered from the disease before 

 it reached their trunks. As above intimated, this process is probably 

 at its height in this area, since suppression of the branches is ap- 

 parently at its maximum. 



Experiments in Control in Europe. 



In experimenting with the white-pine blister rust, the European 

 investigator has always had a different viewpoint from that of the 

 investigator in North America. This has been due to two reasons — 

 the disease was possibly native in Europe, certainly in Asia, but was 

 introduced into North America; Pinus strohus, the favorite pine host 

 for the fungus, is native in North America and introduced into 

 Europe. That is, the situation is exactly reversed in every respect 

 in North America as compared with Europe. 



The disease is generally considered to have been native in the 

 Alps and in the Ural Mountains upon Pinus cembra. It appeared 

 in widely separated localities through Northern Europe before plant 

 pathology had developed to any extent. That is, organized quaran- 

 tines, present methods of spraying, and many other methods now 

 used in fighting plant diseases were unknown at that time. The 

 fact that the disease was prevalent practically throughout northern 

 EuTope before it became generally known, showed plainly that it 

 was firmly established throughout that region. This meant that 



57 Posey, G. B., and Gravatt, G. F. Op. cit. 



