Mar. 19, 1917 
Dissemination of Angular Leaf spot of Cotton 
469 
yet in another experiment in which cold, poured agar plates were taken 
to the field and with covers removed, dew dashed onto the agar surface, 
about the same percentage gave growths of Bad . malvacearum. 
It is reasonable to expect that the bacteria would become as free in a < 
film of water due to rains as to dew. When bacteria have thus escaped - 
from the interior of diseased areas through stomata (possibly in other 
ways) and have been suspended in this water film, any agency carrying 
this water from plant to plant becomes a means of dissemination. Wind 
during rainfall is the most probable agency which has been active in this 
disease of cotton. Infection by contact of plants is precluded by the 
distance between rows (4 feet) and the height of the plants at the time of 
the first experiment—8 to 10 inches at its beginning and not over 18 
inches high at its close. 
meteorological conditions 
Little can be said concerning the wind during the rainfall which spread 
the disease in these experiments. Future studies are planned in which 
these factors will be more closely observed, and it is hoped to learn what 
variations and what minimum amounts of wind and rain, separately and 
together, will have this effect. It is a fact of record that the wind blows 
during the rainfall of thunderstorms of this region, and it is common 
knowledge that the wind blows violently during the rainfall of West In¬ 
dian hurricanes. As types of the thunderstorms most important in this 
regard, three graphs are presented (fig. 2), records of storms observed at 
the office of the United States Weather Bureau, Little Rock, Ark., and 
Vicksburg, Miss. The high wind preceding the rain, or at its beginning, 
should be noted. It is improbable that this wind at the beginning is 
instrumental in spreading bacterial diseases, but it will be noted that 
later the wind reaches a velocity of 25, 29, and 35 miles per hour during 
periods in the storms when rain is falling heavily and after the foliage 
has been wet for some time. It is extremely probable that winds of 
these velocities blowing during heavy rainfall will serve to disseminate 
such diseases as the angular leafspot of cotton. 
The records of storms in the extreme western portion of the cotton 
belt are used here so that it will be noted that these meteorological con¬ 
ditions are not peculiar to this locality but that such conditions are 
prevalent throughout the cotton-growing States and probably elsewhere 
as well. 1 
DISCUSSION OF AGENCY 
Suitable conditions of wind and sufficient moisture occur during the 
summer rains of this region. The method of action of this combination 
has been and will be the subject of close attention. During June, 1916, 
1 Thanks are due to Messrs. H. S. Cole and William E. Barron, officers in charge of the Weather Bureau 
offices at Little Rock and Vicksburg, respectively, for their kind assistance and suggestions in this phase 
of the subject. 
78367°—17 - 3 
