Journal of Agricultural Research voi. xxiii, No. 4 
276 
It is clear, however, that the conidial stage of Sclerospora, at least in 
the Philippine forms, is far more complex in respect to conidium produc¬ 
tion and dispersal and far more important in disease dissemination 
than has been realized hitherto. 
SUMMARY 
In the Philippine Islands the two downy mildews, Sclerospora phihp- 
pinensis and S. spontanea are in their conidial phases injurious parasites 
of maize. Investigation of the two species has cast light of certain 
hitherto obscure points in: (1) The production and dispersal of conidia, 
and (2) the relation of these processes to the local and distant dissemina¬ 
tion of the diseases. 
Production of conidia on infected plants is preceded by the establishing 
on leaves and sheaths of characteristically discolored areas that in out¬ 
line and pallor are symptomatical of the disease. Production takes 
place chiefly and in greatest quantity on such areas which may occupy 
a relatively large proportion of the plant's surface. 
Conidiophores never develop except from the stomata, at night, and 
when the surface is covered with dew or other moisture. From the 
mycelium in the underlying tissue, branches push through the stomatal 
pores, forming crowded groups of lobed and knob-like outgrowths. 
These elongate, developing successively into mature conidiophores, sev¬ 
eral of which are formed at each stoma during the course of the night. 
The conidia apparently are liberated by active ejection from the sterig- 
mata, rather than by passive disjunction as has been assumed; but fur¬ 
ther investigation is necessary to establish this point. Nocturnal devel¬ 
opment of conidiophores in the usual amount of dew follows a relatively 
regular cycle, which, however, may be altered by rain or by drying 
winds. 
Conidia are produced in vast numbers, even a small plant liberating a 
quantity sufficient to infect the neighborhood. The number produced 
on a plant during one night chiefly depends on the extent of the produc¬ 
tive surface, on tie number of stomata in this surface, and on environ¬ 
mental conditions. Approximate estimates of the number produced on 
representative plants of different ages are given. 
Production of conidia on an infected plant is not limited to one night 
but may be repeated on successive nights when conditions are favorable 
over a period covering as much as 75 per cent of the total life of the 
plant. The duration of production in the case of several different varie¬ 
ties of infected maize is given. 
Dispersal of conidia takes place necessarily at night. (1) It is accom¬ 
plished chiefly by wind. Slight air currents are especially important; 
because, although local, they occur very frequently and at the time of 
maximum conidiophore production. Stronger breezes, usually near the 
sea and on broad plains, are effective because they occur often during 
maximum conidiophore production and cover considerable territory. 
Violent gales are not conducive to copious and general production of coni¬ 
dia but yet are important, because they rapidly sweep such few conidia 
as may be formed over great distances. (2) Dispersal of conidia is also 
accomplished by splashing. Drops of dew or rain falling on the conidi- 
ophore-bearing leaves, splash off, laden with conidia, and may reach 
young maize directly or may be carried to it by wind. (3) Dispersal is 
