Jan. 27,1923 
Production of Conidia in Philippine Sclerosporas 269 
From his investigations it seems safe to assume that in the downy mil¬ 
dews of maize splash distribution would be accomplished as follows: 
Drops of dew dripping upon moist spore-bearing leaf surface only 12 
inches below would scatter droplets full of conidia over an area 20 to 
32 inches in diameter. Raindrops falling from a height of only 16 feet 
upon such leaf surfaces 4 feet above ground would spatter droplets 
containing conidia for a distance of 3 feet 2 inches if the leaf was level 
or as much as 5% feet if the leaf surface inclined 30°. Droplets spat¬ 
tered thus from a leaf 4 feet above the ground would be carried as much 
as 18 feet by a wind blowing 10 miles an hour and proportionately 
farther by winds of greater velocity. Also conidium-containing droplets 
would be relayed on from plant to plant by splashing and by wind through¬ 
out the duration of a storm. Faulwetter (9) demonstrated that spat¬ 
tering and wind-blown rain were important factors in the dissemination 
of the angular leaf spot of cotton. The writer, from a study of the 
maize downy mildews of the Philippines, is convinced that these factors 
are operative in their distribution also. 
The two methods thus far considered—namely, wind distribution and 
splash distribution acting either separately or together—are the main 
instruments in achieving dispersal of conidia of the maize downy mil¬ 
dews under Philippine conditions. 
DISPERSAL BY AGENTS OF MINOR IMPORTANCE 
Surface water apparently accomplishes conidium dispersal to some 
extent by washing the conidia which fall in it into contact with young 
seedlings which are temporarily submerged. Although this was not 
shown to take place by direct experiment, nevertheless there is consid¬ 
erable evidence of infection occurring in this manner. When glass 
dishes containing brook water and rain water were exposed at nights 
under plants producing large numbers of conidiophores, great quantities 
of conidia were caught. Some of these floated while others sank, but 
all germinated vigorously. When these dishes were exposed to the 
sun the conidia were soon killed, probably by the rapid increase in the 
temperature of the water. When the dishes were protected from the 
sun, however, the conidia retained their vitality and continued to ger¬ 
minate and grow until some hours after dawn. Young, susceptible 
plants, inoculated with a concentrated suspension of living conidia from 
these dishes, soon developed the disease. Moreover, in the field it was 
frequently noticed that during the rainy season low-lying plots often 
became submerged under a few inches of standing surface water at a 
time when the maize had just germinated and the young seedlings were 
in their most susceptible stage. Extremely heavy infection generally 
resulted in these inundated areas, the remainder of the field being much 
less affected. This was also observed by Baker (1) who wrote: 
In one interesting case, a part of a field had been subjected to wash during a heavy 
storm just after planting. On this area every plant was taken by the mildew, while 
in the remainder of the field not a half dozen died. 
Insects also contribute somewhat in conidium dispersal. While 
diseased corn plants were being examined at night, insects were often 
seen crawling about on the conidium-bearing leaves and passing indis¬ 
criminately from plant to plant. In spite of the fact that many insects 
are not active at night and that even the nocturnal ones are kept away 
