53 

 GROWTH ON OTHER MATERIALS THAN CHESTNUT. 



Iii the laboratory the fungus grows well on a variety of artifi- 

 cial media, perhaps most readily 011 potato agar that has been 

 made slightly acid. Material was submitted to us of white oak 

 and black oak bark, collected by Mr. J. K. Guyer, agent of the 

 Pennsylvania Commission, which bark had been killed by fire pre- 

 vious to its observation, and SIUA\I-.. pustules of what seemed to 

 be Diaporthe parasitica. Careful microscopic examination show- 

 ed that the morphological features corresponded closely to those 

 of DiaportJie parasitica, as did also the growth of the fungous in 

 artificial culture. lied oak twigs killed by steaming in the process 

 of sterilization, were readily infected by Diaporthe parasitica ob- 

 tained from a typical chestnut lesion. While it is desirable to 

 carry on further cross inoculation experiments, it seems rea- 

 sonable to suppose, iii the light of present evidence, that Diapor- 

 the parasitica may, under unusual circumstances, establish itself 

 saprophytically on portions of trees outside the genus Castanea, 

 if these portions are already dead. We have found no evidence 

 that the fungus produces in any sense a disease of such trees as 

 (lie oak. 



RELATION TO LIGHTNING INJURY. 



In August, 1908, Mr. George Wirt, of the Pennsylvania For- 

 estry Department, directed the attention of the speaker to a 

 chestnut tree in an advanced stage of infection, that had been 

 struck by lightning earlier in the season, when its leaves were 

 half grown. Where the wood had been splintered along the 

 lightning track, there were numerous pycnidia standing apart 

 one from the other, as is characteristic of Diaporthe parasitica 

 when fruiting on wood rather than on bark. Many of these fruit- 

 bodies were deep in the cracks made by the lightning, and evi- 

 dently had been formed after the stroke. Specimens taken from 

 the wood and from the bark near by, when tested, gave good 

 germination of spores. Probably the bark infection, which 

 seemed to date far back, existed at the time of the stroke, and the 

 fungus spread from this to the shattered wood, the lightning 

 presumably not having killed the fungus in the vicinity. 



