240 
Journal of Agricultural Research voi. xxiii, no. 4 
two closely related but specifically distinct conidial Sclerosporas were 
causal there. One of these, Sclerospora spontanea Weston, occurs on 
maize and the wild grass Saccharum spontaneum L. in the Visayan Islands 
and is particularly distinguished by its long, slender conidia; while the 
other, Sclerospora philippinensis Weston, occurs on maize in the Island 
of Luzon and has relatively short conidia. Papers describing the char¬ 
acteristics and discussing the destructiveness, distribution, and relation¬ 
ship of these species already have been published (24, 25). 
In the course of this work the process of conidium production and dis¬ 
persal has been worked out; and as this phase of the life history of Sclero¬ 
spora has never before been investigated in detail and shows several 
points which are of considerable importance in their relation to control, 
and of some interest from their mycological aspect, these are presented in 
the following paper. 
PRODUCTION OF CONIDIA 
As has been reported previously by the writer (24, 25), the conidial 
stage is the important one in the life history of the Philippine maize mil¬ 
dews, as it is by means of this stage exclusively that the widespread and 
serious destruction of maize is accomplished in the Philippine Islands, 
the oospores being as yet unknown on this host. The most vital phase of 
the conidial stage is the complex and hitherto obscure process of conidio- 
phore and conidium production. Detailed consideration of this matter 
necessitates discussion of the following points: the demarcation of the 
conidiophore-bearing areas through preliminary paling of the infected 
tissue; the influence of environmental conditions, especially moisture, in 
inducing conidiophore production on these areas; and the emergence and 
development of the conidiophores thus induced. In addition, the noc¬ 
turnal cycle of conidiophore development under various conditions, the 
long duration of this production in relation to the life of the host, and the 
magnitude of the numbers of conidia produced will be considered. Be¬ 
cause the two causal species of Sclerospora agree essentially in all the 
main features of conidium production, the following account of the process 
except as noted applies equally to both. 
PRELIMINARY PAUNG OF THE CONIDIOPHORE-BEARING AREAS 
When a maize plant becomes infected with Sclerospora, it first develops 
on the normally green leaves markings of a more or less conspicuous pale 
yellowish white color {PL 1 B), and later it shows on the areas thus marked 
a down or felt of innumerable conidiophores and conidia {PL 1, A ). These 
etiolated markings are always present in infected plants but vary greatly in 
extent, in shape, and in color according to the effect of such factors as the 
individual and varietal character of the host, the age at which it became 
infected, and the kind of climate and soil which have influenced it subse¬ 
quently. As a result, it is not possible to cover the range of variation by 
any general description of the markings. To be sure, they may be 
grouped roughly into such categories as the types 1,2, and 3 recognized 
by Palm {16) in the Javan maize mildew; but it should be remembered 
that these types are not differentiated with absolute distinctness, but 
intergrade. 
Certain types of markings are not associated with conidiophore produc¬ 
tion and hence need not be considered here. Palm's third type, with 
slender golden striping decreasingly extensive on successive leaves, and 
the markings of similar characters found by the writer (25) to result from 
