Mar. 8,1924 
Nocturnal Production of Sclerospora 
773 
whitish patches of shriveled conidiophores persisting on the leaves from 
previous productive nights, indicated that the plants were still support¬ 
ing conidiophore formation under favorable conditions. Frequent care¬ 
ful inspection of these plants throughout the day of July 23, however, 
showed conclusively that, during this daytime at least, no conidiophore 
production took place. Accordingly, in the late afternoon, the plants 
were prepared for night study by removing from the leaves all remnants 
of previous conidiophore production by carefully scrubbing the surface 
with moist cotton swabs. That night, beginning at about 8 p. m., when 
dew deposition commenced, the plants were examined at hourly inter¬ 
vals and were found, indeed, to produce conidiophores in abundance. 
By cutting free-hand sections of living, infected leaves, stripping off 
bits of epidermis, macerating pieces of tissue, and carefully scraping off 
the down of conidiophores as it developed, the process of conidiophore 
emergence and conidium production through the night was followed 
step by step in detail. After production had ceased, as the plants dried 
off in the early morning of the next day, periodic examination of the 
plants was continued until afternoon; and this again brought out the 
fact that no conidiophores were produced during the day. The fact 
that in Sclerospora graminicola conidium formation does indeed occur 
at night was established by these observations; but in order to supplement 
them, as they extended over two days and one night only, the most 
vigorous of the infected Setaria plants were transplanted to Washington, 
D. C., where they were studied further. 
The process of conidiophore production involves, as the writer found 
in the conidial Philippine Sclerosporas, the following phases: The pre¬ 
liminary paling of the leaf areas which are to bear conidia, the quantity 
of conidia produced on such areas, the length of time this production 
may go on night after night, the importance of moisture in inducing 
conidiophore production, the development of conidiophores and conidia 
thus induced, and the nightly schedule followed by this development. 
The writer did not have opportunity to work out in detail these several 
points for 5 . graminicola as he did in the Philippine Sclerosporas, but 
studied chiefly the development of the conidiophores and conidia, the 
nightly schedule followed by this development, and its dependence on 
dew or similar moisture. The results of this study follow. 
DEVELOPMENT OP THE CONIDIOPHORES 
The conidiophores of Sclerospora graminicola develop from the infected 
Setaria leaves only through the stomata, a large proportion of which may 
be productive. Consequently, conidiophore production is usually more 
abundant from the under surface of the leaf where stomata are more 
numerous, although this abundance is dependent also on other factors 
such as the amount and distribution of dew on the leaf and the length 
of time successive nocturnal production from the plant has gone on. 
Beneath stomata from which conidiophores are to emerge, the air cham¬ 
ber is filled with stout, irregularly lobed, densely granular, mycelial 
branches closely crowded together (PI. 1, A, B), arising from the less 
conspicuous mycelial strands running between the mesophyll cells. From 
these substomatal knots, prolongations push through the stomatal slit 
over which they form a compact group of several minute bulbous out¬ 
growths. In some cases there is evidence that the stomatal slit, normally 
•closed at night, is forcibly pushed open by these emerging branches 
