250 
Journal of Agricultural Research voi. xxiii, no. 4 
discharge. However, in so far as could be determined by a study of 
conidiophores mounted in all stages before and after discharge of the 
conidia, the process apparently takes place as follows: At the point where 
the maturing conidium is attached to the sterigma, the wall across the 
base of the conidium and that across the apex of the sterigma are, when 
first formed, quite flat in contact with each other. Later the increasing 
turgidity of the conidium and sterigma causes these membranes to bulge 
outward, a tendency which is restrained by the adhesion of the two sur¬ 
faces to each other. As this impulse to bulge outward increases more 
and more, however, it finally reaches a point where it overcomes the 
adhesion of the two surfaces; and with a sudden snap the basal septum 
of the conidium and the apical septum of the sterigma bulge sharply 
outward and shoot the conidium away. In abundant fresh material all 
the stages of this process can be traced, the flatness of the base wall of 
the conidium and the apex of the sterigma before (PI. 9, L-V), and the 
bulging after discharge, being particularly noticeable. 
Apparently all the conidia on one conidiophore customarily are ejected 
at once; but occasionally a conidiophore was encountered with most of 
its sterigma tips bulged out and obviously just freed from their conidia; 
while on one or two branches seemingly less mature, the conidia still 
remained in situ (PI. 9, W). 
When the conidiophore has discharged its conidia, its vitality declines, 
it is attacked by bacteria which swarm in the moisture on the leaf sur¬ 
face, and after dawn it is shrivelled by the sun to a dry, almost unrecog¬ 
nizable mummy (PI. 10, C, D, E, H). In no case was seen any evidence, 
such as sterigmata with their apices burst open, which would indicate 
that an explosive ejection of the conidia, with loss of contents and subse¬ 
quent collapse of the conidiophores, had taken place. 
The discharge of conidia by the sudden bulging out of walls formerly 
flat in contact with each other was first described according to Buller (2) 
by Nowakowski for the Entomophthoreae. It has since been found by 
Buller (2) to take place in the case of the basidiospores of certain Hymeno- 
mycetes, and by Coons (5) also in the case of the sporidia of Gymnos- 
porangium. In view of this, it is of interest to note that a similar method 
of spore discharge apparently obtains in the genus Sclerospora of a 
family (Peronosporaceae) in which the passive abjunction of the conidia 
has been assumed hitherto. 
The distance which the Sclerospora conidia are ejected is very minute. 
With the apparatus available no accurate measurements could be made; 
but by such crude devices as the slanting slide mentioned above, the 
trajectory limit was approximately determined as about 1 to 2 mm. 
Small as this distance is, however, it suffices to carry the conidia into the 
air where they are wafted away by more or less rapid air currents; and it 
is noteworthy that this process of conidium discharge is remarkably well 
adapted to secure the dispersal by air currents of conidia flung from the 
moist surface of the maize plant. 
NOCTURNAL CYCLE OF CONIDIOPHORE PRODUCTION 
The process of conidium production which has been described follows 
a regular cycle under normal conditions of dew deposition. The leaves 
are wet with dew at 8 or 9 p. m. Groups of knoblike initials are formed 
over the stomata at about 11 p. m. and most of the first “ crop ” of conidia 
