9 



differences, so we feel justified in referring the parasite to the 

 species originally described by Saccardo and Winter. The 

 causal relation is based not only on the constant association of 

 the fungus with the disease but also upon successful inocula- 

 tions in the field. That Strumella coryneoidea was not connected 

 with the disease by Dr. Buckhout^ is evident from his statement 

 that the disease is "apparently of the same nature if not identical 

 with Mectria diUssima, the canker of the apple tree." 



The fruiting stage. — During the time previous to the girdling 

 and consequent death of a branch or trunk, the fungus produces 

 only mycelium and aborted or rudimentary fruiting pustules. 

 As soon as the girdling has been completed, however, an abund- 

 ance of fertile pustules appear in the form of brownish 

 erumpent powdery cushions, the sporodochia, scattered either 

 sparsely or abundantly over the surface of the invaded por- 

 tions and also beyond the extent of the original lesion (figs. 8 

 and 18). 



The sporodochia vary in size from 1-3 mm. in diameter (fig. 

 19), and each consists of a dense aggregate of fungous tissue 

 which bursts through the external cork layer in the form of a 

 • rounded nodule which produces over its entire free surface a 

 multitude of erect, branched, spore-bearing hyphae or conidio- 

 phores. Spores are developed in profusion from the terminal 

 portions of the brownish conidiophores (fig. 20), and either 

 loose or attached, give the granular or powdery appearance to 

 the fruiting pustules (figs. 8 and 18). The spores (fig. 21) are 

 light or very dark brown, single-celled, vary from nearly glob- 

 ular to pear-shaped or irregular in form, and vary in size from 

 5.1 — 13x4 — 7.3 mikrons. No ascus stage has been found in 

 the life cycle of this fungus, but the profusion of conidiospores 

 would appear to offer an effective means of dissemination. As 

 the accumulated spore mass is powdery when dry it seems prob- 

 able that wind dissemination is one of the important means 

 of spread of the fungus. The loose spores are undoubtedly 

 washed down by rains. The latter statements are based however 

 on observational evidence rather than on direct experimental 

 evidence. 



S. Loc. cit. p. 250. 



