^54 
Joxvrnai of Agricultural Research 
Vol. XXIV, No- lo 
and sugar-cane mildew of Queensland, Fiji, Formosa, and the Philip¬ 
pine Islands; and of Reinking (jo) and Weston (74, 15, 16) on the 
maize mildews of the Philippines, our knowledge of these forms is fairly 
complete. We know that if they should be carried to the United 
States on maize seed, it would be by resistant mycelium within the 
seeds, or by conidia or oospores on them. That mycelium should be the 
means is most improbable. Palm's work on the Javan maize mildew 
and unpublished experiments of the writer on the Philippine mildew of 
maize show that in the case of these two Sclerosporas at least, mycelium, 
although frequently penetrating the seed of badly infected ears, appar¬ 
ently is unable to transmit infection to the seedling developing therefrom. 
In such vegetative propagative parts as cuttings of sugar cane, living 
mycelium of Sclerospora may be carried and transmitted; but, in the 
case of maize, which is propagated only by seed, this difficulty is avoided. 
Conidia adherent to maize seed can not accomplish infection. In the 
Philippine maize mildews the writer has found that conidia do not sur¬ 
vive drying even for as short a time as one hour. Butler {2) in India 
and Miyake (7) in Formosa find this to be true of the maize mildews of 
those countries also. 
It is preeminently probable that oospores on or in the maize seed can 
transmit infection. In the case of the closely related downy mildew of 
millet {Scl^ospora graminicola [Sacc.] Schroet.) there is every ^evidence 
that intercontinental spread has been accomplished in this way. Whether 
the same means of distribution operates in the maize Sclerosporas we 
do not know. It should be noted in this connection that, although none 
of the several oriental mildews of maize has ever been found to produce 
oospores on maize itself, nevertheless these resting spores may occur 
abundantly on related hosts from which they can reach adjacent maize 
plantings. 
Since the conidia are so easily killed, it will be by the resistant oospores, 
if at all, that these downy mildews will be introduced on maize seed. 
Consequently seed treatment must be directed against the oospores. 
To be effective in the case of Sclerospora diseases, a method of seed treat¬ 
ment not only must destroy any of these resistant spores which may be 
present but also must meet certain unusual requirements. The efficacy 
of the usual types of seed treatment is customarily demonstrated by the 
failure of adherent spores to give growth of the disease-producing fungus 
when the treated seeds have been placed in suitable media. But this 
would prove no index in the case of Sclerospora, as germination of the 
oospores has never been seen, and growth of the fungus on artificial 
media has never been secured. To ^ successful for Sclerospora, then, 
a method must give conclusive visible evidence of the destruction of the 
oospores. 
EXPERIMENTS IN SEED TREATMENT 
With this end in view, experiments were made with the substances 
customarily used in seed treatment. Of these, concentrated sulphuric 
acid fulfills the requirements most successfully, since it gives visible 
evidence of oospore destruction and yet does not impair seed germina¬ 
tion. This was determined as follows: 
Oospores (both fresh and two years dried) of the Sclerospora species 
so common (74, 75) on Saccharum spontaneum L. and Miscanthus japoni- 
cus (Thunb.) Anders, in the Philippines were mounted on a slide and 
carefully observed through the microscope while a drop of concentrated 
