AUTOBASIDIOMYCETES 



441 



distortions on young shoots of Andromeda lignstrina. Galls of 

 this latter form are hollow, bag-like structures which may attain a 

 length of five or six inches. 



Richards employed the large form on Andromeda and Exo- 

 basidium Vaccinii in some cross inoculations and was able to 

 develop the leaf spot form of the gall on Andromeda from Exo- 

 basidium Vaccinii, and also to produce this same form through 

 spores from the galls on Andromeda. He also directs attention 

 to the fact that the larger distortions in 

 general are produced only during the 

 early part of the year, that is, when the 

 fungus attacks* the young and sensitive 

 tissue. Cross-inoculation work is at- 

 tended with some difficulty on account 

 of the diversity in season of the vari- 

 ous forms, and probably also differ- 

 ences in the susceptibility of the hosts 

 as the season advances. 



The fungus. The hyphse are fine, 

 much branched, and commonly inter- 

 cellular. They are most abundant in 

 the subepidermal layers, and in the case 

 of the forms producing galls upon the 

 young stems they are more or less con- 

 fined to the cortical parenchyma. The 

 basidia arise directly from the hyphae, 

 pushing up between the epidermal cells. A basidium bears fre- 

 quently four spores, but two to seven may be produced. The spores 

 are elliptical or slightly curved and ordinarily measure 14-17 X 3 /*. 

 Among the basidia, at intervals, may appear certain branched 

 conidiophores bearing small acicular conidia. This is apparently 

 the chief conidial type in the genus Exobasidium. 



Fig. 216. Exobasidium Vaccinii 

 (After Woronin) 



III. HYMENOMYCETALES 



Among the higher Basidiomycetes the important forms from 

 the view point of the economic plant pathologist are included in 

 a few families of the Hymenomycetales. This order includes the 



