ASCOMYCETES 



275 



adheres closely to the underlying wood. Moreover, tne develop- 

 ment of a callus layer at the edge of the dead spot gives a further 

 emphasis to the depression produced by the death and shrinking 

 of the tissues within the canker spots. The canker spots are sup- 

 posed to persist for at least two years. The mycelium of the fun- 

 gus may be found in the inner bark and cambium. As previously 

 suggested, the pustules of the fungus break through the bark in 

 these cankered spots early in 

 the season. 



When the fruit spots have 

 attained a size of one fourth 

 inch or more in diameter, 

 there may appear in concen- 

 tric lines small papillae, which 

 are in reality the pustules of 

 the fungus. The pustules are 

 formed by the development of 

 a stromatic mass of mycelium 

 beneath the epidermis. From 

 this stromatic mycelium there 

 develops a cone-shaped mass 

 of erect hyphae which eventu- 

 ally rupture the cell walls. 

 Meanwhile there are produced 

 from the numerous, erect 

 conidiophores an abundance 

 of conidia. When the epider- 

 mis is ruptured, these conidia emerge as a waxy, tendril-like strand, 

 which may be at first pink in color, becoming gray with age. The 

 spores are then imbedded in a gelatinous matrix readily soluble in 

 water. Little may therefore be seen of the strand-like production 

 of the spores during moist weather, or even during a period of 

 heavy dews. Fig. 124 shows the relation of the conidiophores to 

 the mycelial stroma. Examined microscopically the conidia are 

 almost hyaline, though having a slight greenish cast. They vary 

 in shape from ovate to oblong, or in some cases even slightly 

 dumb-bell-shape. In general, however, they are ovoidal and vary 

 greatly in size, according to the conditions under which they are 



FIG. 123. CANKER OF THE BITTER ROT 

 FUNGUS. (Photograph by Perley Spaulding) 



