72 BULLETIN 380, U. S. DEPARTMENT OF AGRICULTURE. 



ward by the advocates of the " weakened host " theory seems to be 

 fully established; that is, that the chestnut trees have suffered se- 

 verely in the southern Appalachian regions previous to the present 

 epidemic, in some cases being practically exterminated, so that the 

 range is now considerably less than formerly. The evidence on this 

 point has been summarized by Clinton (18, pp. 408-413). Various 

 writers quoted by him cite fire injury and borers and other insects 

 as -causes for this recession. 



Long (48, p. 8) considers a root rot due to ArmAllaria, mellea as 

 " very probably an important factor in the gradual recession of the 

 chestnut" in North Carolina. It seems probable that all of the 

 above-mentioned factors, and perhaps others, have played a part in 

 the destruction of the chestnut in this region. 



RELATIVE SUSCEPTIBILITY OF SPECIES OF CASTANEA. 



The importance of Castanea dentata as a timber and nut tree and 

 its abundance in eastern North America, where the blight is preva- 

 lent, has made the chestnut blight an object of much investigation. 

 Descriptions of the nature and importance of the disease, the rate 

 of its spread, methods of distribution, and attempted methods of 

 control have been given in detail by Anderson (1-5) , Clinton (12-15) , 

 Heald (39-41), Metcalf (51 and 52), Metcalf and Collins (53), Ran- 

 kin (62), and others. It may be sufficient here to state that the 

 fungus enters the host through a wound in the bark, probably never 

 or very rarely through lenticels or natural cracks, grows chiefly in 

 the cambium, penetrating for only short distances into the wood, 

 and kills the tree or branch by girdling. Once a tree is attacked, 

 it is only a question of time till it succumbs. 



The chinquapin (Castanea pumila) was found by Murrill (58) in 

 1908 to be attacked by Endothia parasitica. Rogers and Gravatt 

 (65) in 1915 made inoculations of E. parasitica on C. pumila and 

 found that the parasite grew as rapidly on this host as on C. dentata. 

 They attribute the apparent resistance of the chinquapin to its com- 

 parative freedom from bark injury, a view also held by other writers. 

 Pantanelli (60) and Metcalf (52) have proved that the European 

 chestnut is readily susceptible to the disease. 



The only chestnuts thus far observed which show an}^ resistance 

 to Endothia parasitica are those of oriental origin. Metcalf (51) 

 first pointed out the resistance of the Japanese chestnut. This 

 observation has since been confirmed by Clinton (18, p. 375), who 

 " failed to produce the disease in a Japanese variety in the [Conn.] 

 station yard, although the bark was inoculated in 16 different places." 



Van Fleet (84), in describing the spread of the chestnut blight in 

 his breeding plats at Washington, D. C, says (p. 21) : " The Asiatic 

 chestnuts and the chinquapin-Asiatic hybrids are plainly highly 

 resistant." 



