jan. 27,1923 Production of Conidia in Philippine Sclerosporas 249 
able conidia. If the conidia merely dropped off the sterigmata, they 
would of course fall down to the Petri dishes from the lower surface of 
the more or less horizontal leaves; but those produced on the upper 
surface would hardly be carried off by the slight convection currents 
within the jar rapidly enough to prevent most of them from falling into 
the moisture on the upper surface of the leaf. Microscopic examination 
of the moisture on the upper and lower surfaces of the horizontal portion 
of such a leaf, however, showed no more spores in the former than in 
the latter, and relatively very few in either. Moreover, a whitish deposit 
of innumerable conidia often was observed on healthy leaves which, 
in crowded plantings, stood in close juxtaposition to infected, spore¬ 
bearing leaves. This occurred even when the parts were sheltered and 
were in such a vertical or oblique position as to preclude the possibility 
of such a deposit accumulating from conidia which merely fell. 
From such observations the writer was led to suspect that the conidia 
were actively discharged. To obtain further information on this point 
the following experiments were performed on maize infected with Sclero - 
spora philippinensis. During the afternoon the leaf of a badly diseased 
plant that was known to be producing abundant conidia each night was 
carefully scraped with a scalpel until its surface was entirely free from all 
dried remnants of the last night’s conidiophores. The leaf was then fas¬ 
tened to a stake so that this scraped surface was held rigidly in a vertical 
plane. Facing this surface a slide, previously smeared lightly with clear 
agar, was fastened securely at a very slight angle, with the upper end 
almost touching the leaf and the lower end about 3 mm. away. The 
earth around the plant was then watered copiously; and the whole was 
covered with a large tin can the edges of which were pressed firmly into 
the earth and sealed with wet clay. Early the next morning this cover 
was removed carefully so as not to disturb the plant; and the slide was 
dexterously lifted away without touching it to the leaf surface. On ex¬ 
amination the slide was found to be covered with freshly germinating 
conidia for some distance from the edge nearest the leaf. By substitut¬ 
ing a strip of black cardboard for the slide, a faint spore-print, decreas- 
ingly dense toward the end farthest from the leaf, was obtained. 
More direct evidence was secured as follows. Under a strong beam of 
light concentrated by a condenser, a portion of the leaf surface where 
abundant conidium production was taking place was watched contin¬ 
uously through low power magnification. Under these conditions the 
conidiophores, their tops heavy with clumps of maturing conidia, could 
be seen standing in rows corresponding to the rows of stomata below. 
During long observation occasional clumps of conidia were seen to flash 
away as momentarily gleaming specks, leaving a gap in the line of conidi¬ 
ophores. 
In the opinion of the writer these experiments and observations indi¬ 
cate that the conidia are forcibly thrown off from the sterigmata. It will 
rest with future and more precise investigations to prove this conclu¬ 
sively. 
Attempts were made to determine the means by which discharge of the 
conidia was accomplished. Because all efforts to grow the Sclerosporas 
in pure culture failed, it was impossible to study the developing conidio¬ 
phores in Van Tieghem cells; and it was found equally impossible to 
adjust conidiophore-bearing leaves for study under the high power with¬ 
out disturbing the moisture on the leaf and interfering with conidium 
