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



are much more severely attacked in the Chekiang Province than 

 either in Chihli, Shansi, or Shensi. Could the greater humidity of 

 central China be of assistance to a more vigorous development of 

 this destructive fungus?" 



COMPARISON OF HOST RELATIONS. 



It will be seen from the above description of the host relations of 

 the various species that while some other members of the genus 

 (E. gyrosa, e. g.) may have slight parasitic tendencies, Endothia 

 parasitica alone is an active parasite. The contrast is still more 

 striking in the section of the genfts to which E. parasitica belongs, 

 for E. fluens and E. fluens mississippiensis, which resemble E. para- 

 sitica so closely in their morphological characters, and to a less 

 degree on culture media, and are common on Castanea, are almost 

 purely saprophytic. This fact is established by the work of Ander- 

 son (2), Clinton (18), and others, and by two years' field observa- 

 tions and several thousand inoculations made by the writers and 

 their colleagues. 



The host relations of the parasite are equally striking. Although 

 Endothia parasitica is so pathogenic on Castanea dentata that this 

 tree has been practically exterminated over several hundred square 

 miles of its natural range and its extinction is threatened, the fungus 

 has been only occasionally found as even a weak parasite on the 

 closely related genus Quercus, and never, to the writers' knowledge, 

 on Fagus. 



During the course of this work the writers have been continually 

 impressed with the possibilities of a physiological study of E. para- 

 sitica and one or more closely related species which might throw 

 some light on the fundamental question of the nature and cause of 

 parasitism. No other case is known to the writers of a virulently 

 parasitic fungus and a closely related purely saprophytic one which 

 will grow readily and fruit on a large variety of artificial media, 

 which are readily distinguishable on those media, and remain con- 

 stant for hundreds of generations. 



SUMMARY. 



The pathological and economic importance of this group of fungi 

 was first recognized when the chestnut-blight fungus was discov- 

 ered in New York in 1904. 



This organism was first referred to the genus Diaporthe, but 

 was later shown to belong to the genus Endothia. 



The specific identity, relationships, and native home of this para- 

 site were at first uncertain. Some pathologists considered it a native 

 organism which was attracting attention and causing injury chiefly 



