THE MONTHLY BULLETIN. 



271 



eembra), a relative of white pine With this pine it was probably introduced into 

 western Europe, where the extended nurseries and plantations of white pine fur- 

 nished rich material for its attaeks. It is on 

 nurserj stock of white pine imported from 

 abroad that this Siberian disease was intro- 

 duced into the United States. 



We have here the curious case of an Amer- 

 ican plant, sound in its native country, con- 

 tract ins; an introduced Siberian disease in 

 western Europe, and on its return to America 

 carrying the disease with it. Its presence in 

 the United States became uoticeable in the first 

 decadi of this century, although there may have 

 been isolated cases in earlier years. 



The fact that the white pine blister rust has 

 not appeared al a very much earlier date in 

 western Europe, in spite of an absolute lack of 

 a protective quarantine against Russia in the 

 tirst half of the last century, can only be 

 explained by the absence of susceptible native 

 pines in the forests. Planted wdiite pines at 

 that period were still rather rare and the disease 

 had no chance of establishing itself until it 

 found the ground sufficiently prepared. The 

 case is entirely different in the eastern United 

 States, where white pine covers vast tracts of 

 land and offers ideal conditions for the rapid 

 propagation of the disease. In Europe the 

 entire problem will be solved by excluding white 

 pine again from cultivation and returning to the 

 state of affairs before the introduction of this 

 species which after all never formed an integral 

 part of the European forests. In the United 

 States, on the other hand, one of the most 

 important members of the forest community is 

 in immediate danger, and in addition the related 

 species, amongst others the most valuable pine 

 of the Pacific coast, sugar pine, are jeopardized. 



CAUSE OF THE DISEASE. 



The white pine blister rust is caused by a 

 parasitic fungus belonging to the Uredinea? (rust 

 fungi), a family of which all members are para- 

 sites. The name "rust" is derived from the 

 rusty appearance so commonly found on affected 

 parts of the host plant. This rust consists of 

 heaps of the minute spores or reproductive 

 bodies of the fungus plant, which, when carried 

 on to other susceptible host plants, will germi- 

 nate under favorable conditions, enter the tis- 

 sues of the host plants and by growing in these 

 again produce the disease. In our case the 

 blister rust represents the fungus, while the 

 white pine acts as the host. 



But white pine is not its only host. We have 

 already seen that the fungus occurred on Pinus eembra. Both are five-needle pines; 

 that is. having five needles in a bundle. It is an established fact that other five- 

 needle pines, such as sugar pine (Pinvs lambertiana) and western white pine (Pinus 

 monticola), arc subject to the attacks of the fungus. Most probably all five-needle 

 pines will be found to be susceptible. Other pines, for instance the three-needle 

 pines, to which yellow pine {Pinus i>nntlrrw«i) belongs, are immune. 



The matter is further complicated by the fact that the fungus does not pass its 

 entire life on five-needle pines. The spores formed on pines can not infect other 

 pines. They are able only to infect the leaves of currants and gooseberries, where 



Fig. 78. — White pine seed- 

 ling killed by white pine blis- 

 ter rust. Appearance of bark 

 after death. (Photo. U. S. 

 Department of Agriculture.) 



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