Jan. 27,1923 
Production of Conidia in Philippine Sclerosporas 275 
until finally in the last crop maturing in the early part of the on-coming 
dry season it had penetrated even to relatively remote fields and caused 
them heavy losses. 
Whether the discontinuous spread of the mildews from island to 
island is due to the agency of conidia could not be settled by observation. 
Certain evidence, however, seems to indicate that such distribution does 
occur. The closely aggregated Philippine Islands are idealy situated for 
the dissemination of the downy mildews by wind-blown conidia. Of the 
entire 3,000 islands, about 1,000 are of sufficient size and importance to 
be worthy of agricultural consideration; and these are grouped in an 
irregular triangle extending about 1,000 miles from north to south. The 
n largest of these extend over more than four-fifths of this distance 
and comprise but little less than four-fifths of the total area. Yet the 
distance separating any one of these from the next is not over 20 miles— 
often much less. Moreover, their arrangement is such that typhoons 
and prevailing trade winds have a general lengthwise trend over them. 
Downy mildew of maize is already known from the great Island of Min¬ 
danao at the south, from the Visayan Islands in the center, and from 
Luzon at the far north. Seven of the 11 largest islands are known to 
harbor the disease; and in all probability investigation will show that it 
is established throughout the whole archipelago. That this broad 
distribution has been and is being accomplished, at least in part, by 
conidia blown from one island to another on night breezes seems very 
probable to the writer. Night winds, especially those which come in 
sudden gusts of considerable strength, often have a velocity of 10, 20, or 
more miles an hour; while the gales which distinguish nocturnal typhoons 
frequently reach hurricane velocity. Moreover, especially in the Visayan 
Islands, diseased maize is found in abundance on highlands which unob- 
structedly overlook the intervening seas. It seems probable that conidia 
swept by violent gales from such vantage points would take no longer 
to reach the maize fields of neighboring islands 10 miles distant than 
conidia borne on almost imperceptible air currents would take to drift 
from stunted plants to plates exposed 100 feet away. 
Butler (4), in summing up the general question of wind distribution 
of fungi, concludes that— 
Several [cases] suggest that aerial spread is limited to a few miles, while other [fungi] 
are capable of bigger jumps, possibly 50 miles or (in the case of the oak mildew) even 
more. 
The striking experimental evidence of Hesselman (12), on the other 
hand, shows that pollen grains much larger than conidia may be trans¬ 
ported 30 and even 50 miles by breezes of moderate strength. It should 
be remembered, however, that pollen and the spores of most fungi are 
not so rigidly restricted in time or extent of distribution as are the downy- 
mildew conidia which can not survive drying and must be produced, 
scattered, and reach new hosts within relatively few hours of the night. 
The fact that the writer (25) has found two conidial Sclerosporas on maize 
apparently restricted to different groups of the Philippine Islands must 
also be considered. The writer inclines to the belief that dissemination 
of the maize mildews from island to island by means of conidia has taken 
or is taking place, but until further evidence has been obtained and the 
geographic distribution of these and other species has been worked out 
for the whole archipelago, no final decision on this point can be made. 
