1916] MEINECKE: PERIDERMIUM AND CRONARTIUM 231 



on the basal end of the gall, whilst the swelling at the apical end of very 

 young galls is sometimes more gradual. 



Whether these distinctions are sufficiently important to separate the 

 two forms can only be decided by inoculations. Possibly most of them 

 may be explained by the specific influence of the host. The actual proof 

 for the identity of the two forms is still lacking, although Arthur and 

 Kern 13 now list Peridermium harknessii under P. cerebrum. 



For all the pines growing in association with oaks, it is to be assumed 

 that the connecting Cronartium form may still be discovered. One species 

 of pine that does not enter into this system is Pinus contorta, a tree which 

 in the Sierra Nevada inhabits higher elevations and is particularly 

 common around and on mountain meadows. Although frequently 

 found associated with oaks or Castanopsis, it often occurs in localities 

 sixty to eighty miles and more from the nearest representative of either 

 genus. The infection of Pinus contorta with Peridermium harknessii 

 is no less common in such areas, in fact, in some localities it reaches an 

 extraordinarily high degree. Macroscopically the fungus is identical 

 with Peridermium harknessii on Pinus radiata. It is true, that there 

 are data to be found in the literature regarding great distances that 

 certain spores are able to travel without losing their faculty of infection. 

 Klebahn 14 cites a case in which spruce plants were infected by sporidia 

 of Chrysomyxa Rhododendri from Rhododendron plants over a distance 

 of 6 kilometers (v. Tubeuf) and quotes Thaxter as follows: "although 

 it has been shown that infection from cedars may take place at a dis- 

 tance of eight miles (Gymnosporangium nidus-avis)." In both these 

 cases, conclusive proofs for which it would undoubtedly be difficult to 

 bring, the small and light sporidia are said to have traveled a long dis- 

 tance; in our case the fungus would have to be carried, by means of the 

 large and heavy aeciospores, from pine to oak or Castanopsis for sixty 

 to eighty miles over mountains and flat country, more or less covered 

 by a thick screen of forest trees, and back again the same distance by 

 means of sporidia. In the case of Pinus murrayana in the Northwest 

 this distance must be figured by hundreds of miles. 



The question arises as to the means by which the fungus spreads. 

 Either this fungus on Pinus contorta connects with an unknown alternate 

 host or it is identical with the Peridermium harknessii of Pinus radiata. 

 In this case it must be more or less independent of the supposed alter- 

 nate stage on oaks or Castanopsis and its heteroecism is not obligate. 



The absence of oaks and Castanopsis in many Pinus contorta stands, 

 the relative rarity of Cronartium Quercuum on Quercus agrifolia even in 



13 Mycologia6: 133. 



14 Klebahn. Die wirtswechselnden Rostpilze. pp. 32-33. 



