Patfwgenicity of the Chestnut Bark Disease 63 



knife is thrust obliquely into the bark with the broad side, of the 

 blade facing the tree. Without removing the point the knife- 

 is pulled downward and away from the tree. Several drops 

 of the spore-containing liquid are then dropped from a pipette 

 into the exposed wound back of the knife blade. The tree 

 quickly absorbs these drops so that this has proved a very ef- 

 fective method of introducing spores into the living tissue. Be- 

 tween 80 and 100 per cent of successful inoculations have been 

 secured with the so-called Diaporthe parasitica by these methods. 

 Inoculations made in young trees in very low swampy land in- 

 dicate that high water content has nothing to do with suscep- 

 tibility of the trees or the rate of growth of the canker. The 

 fungus grew just as rapidly in thick bark as in thin bark. Cankers 

 grew as rapidly on low ground as on high ridges. 



Almost a thousand inoculations were made with the "western" 

 fungus with uniform results. The growth of the fungus was 

 limited to the area in which the tissue was killed by the in- 

 oculating process. If it spread beyond this area, it was in the 

 dead bark above the living cambium. A definite even line was 

 visible between the dead and living tissue and no fan-shaped 

 areas of mycelium were present. Inoculations made with asco- 

 spores of the ''western" fungus on chestnut oak developed as on 

 the chestnut, forming "spore horns" on the dead area above the 

 wound. Reisolations were made from these "spore horns" prov- 

 ing the fungus to be the same as that used in the original inocula- 

 tions. From these inoculation tests and from observations made 

 in the field there is no longer any doubt that the "western" fungus 

 is a saprophyte and that it cannot develop into an active virulent 

 parasite like the true blight fungus. While it has not been found 

 in the same region where the eastern fungus is common, yet the 

 inoculations showed that it will not develop parasitic tendencies 

 in a region where the so-called Diaporthe parasitica flourishes. 

 It has been proved by inoculations and observations of natural 

 infections that the true blight fungus develops normally about 

 Connellsville in southwestern Pennsylvania. 



TAXONOMY OF THE CHESTNUT BLIGHT AND RELATED FUNGI. 



The taxonomic position of the true chestnut blight fungus 

 and the related fungi has been a question about which consider- 

 able discussion has centered. Since the true bark disease was 

 first described as Diaporthe parasitica in 1906 the generic and 

 specific identity of this organism has been under consideration. 

 Studies of its life history have indicated that it is not a typical 

 Diaporthe. In this connection Shear (16) says that cultures 



