180 BOTANICAL GAZETTE [MARCH 
The conidial layer develops on the stroma which is found on 
the upper surface of the leaf above the base of the young perithecium 
(fig. 14). It may cover only a portion of the stroma, and there 
may be two or even more of them on a single one of the stromata. 
Again, a stroma may develop, to all appearances identical with 
those formed above the bases of the young perithecia, but the 
perithecium be lacking. In this case the conidial pustule invariably 
covers the entire surface of the stroma. Moreover, in the case of 
the first pustules formed in the spring, there is usually little or no 
stromatic base present. 
The conidial pustules are quite irregular in outline (fig. 18), 
although usually approaching a somewhat circular shape. Unless 
two or more of them coalesce, which frequently, in fact usually, 
happens, they may become considerably elongated and variously 
lobed. The size also varies to a considerable extent, due to the 
coalescing of a number of different pustules. The average size is 
about o.5 mm. in diameter, although they may be considerably 
smaller, and have been seen as large aso.8mm. ‘The upper layers 
of cells of the subcuticular stroma elongate in a direction at right 
angles to the surface of the leaf and form the conidiophores. These 
press closely against the cuticle and lift it up somewhat in the 
course of their development. At the same time they give off a 
brown coloring matter which is deposited on the inner or lower side 
of the cuticle, which itself remains colorless. This coloring sub- 
stance is deposited more deeply at the points between the conidio- 
phores than directly above them, so that the darkened cuticle 
presents a somewhat reticulate or netted marking, and on casual 
observation appears to be composed of fungal tissue. This gives 
the impression that the conidial pustule is of the nature of a di- 
midiate pycnidium. Closer observation, however, shows that no 
fungal hyphae enter into this covering layer, and the structure . 
consequently is found to be melanconiaceous in character. The 
deposition of coloring matter on the cuticular coverings of such 
acervuli has been noted by KLEBAHN in connection with the conidial 
stages of Gnomonia padicola (23), G. leptostroma (22), and Gnomont- 
ella tubiformis (24). As previously stated, the same substance is 
deposited between the cells of the hyphae which make up the 
