248 
Journal of Agricultural Research voi. xxiii, no. 4 
more. The process is, however, a continuing one, the knoblike conidi- 
ophore initials developing into conidiophores one after another in fairly 
regular succession so that several stages of the transition from the 
initials to the completed conidiophore are usually found over a stoma 
<P 1 . 7, F; 10, G, H). 
In many cases the first “crop” of conidiophores which matures seems 
to be the maximum one, successive “crops” being somewhat less heavy. 
When badly infected leaves are examined at the time of maximum 
conidium production (usually about 2.30 a. m.) they are seen to present 
a striking appearance. The moist surface is covered with a dense 
grayish white “down” of innumerable conidiophores whose treelike 
shape can be distinguished on closer inspection. 
Attempts were made to determine whether the groups of knoblike 
processes over the stomatal pores were renewed each night by growth 
from the internal mycelium, or were able, if not entirely used up in 
developing conidiophores during one night, to survive the day and form 
conidiophores the night following. In occasional instances, especially 
in Saccharum spontaneum with its sunken, protected stomata (PI. 7, H), 
and during rainy or cloudy days, leaves sectioned during the day showed 
groups of knobs that were apparently still viable. As a rule, however, 
indications were that these groups dried up and were replaced by new 
ones which pushed out of the stoma on the next favorable night. Further 
investigation is necessary to settle this point conclusively. 
It is noteworthy that the tips of the conidiophores customarily pro¬ 
trude slightly from the surface of their layer of moisture on the leaf, so 
that the conidia and sterigmata and perhaps even the ultimate branch 
tips are free, although beaded with adherent droplets of moisture or even 
covered by a single larger drop which involves the whole head. To 
some extent there is apparently a relation between the thickness of the 
moisture layer on the leaf surface and the height of the conidiophores. 
In scanty dew when the layer of moisture on the leaf is very thin, the 
conidiophores are short and stocky; while those which develop in deeper 
layers of heavy dew are usually longer. In both cases the conidia are 
borne just above the surface of the moisture layer. It should be noted, 
however, that the specific distinctions of length which exist between the 
conidiophores of Sclerospora philippinensis and 5 . spontanea are not 
invalidated thereby; since especially in their longer and more slender 
foot cells the conidiophores of the latter maintain their proportionate 
differences even when the two are grown under the same conditions 
(PI. 8, O, P; 10, B, F). 
DISCHARGE OP THE CONIDIA 
In view of the fact that the conidia were borne just barely above 
the surface of the layer of moisture on the leaf, or even involved in 
adherent droplets, and yet (as will be shown later) were distributed in 
vast numbers by the slightest air currents, it did not seem possible to the 
writer that mere passive adjunction of the conidia from the sterigmata 
could be accountable for all that was observed. When, for instance, 
Petri dishes containing a thin layer of nutrient agar were placed at the 
base of a young, infected, corn plant from which abundant conidium 
production took place nightly, and when the whole was covered by a large 
bell jar firmly pressed into the earth and allowed to remain overnight, 
in the morning the surface of the agar was found covered with innumer- 
