Mar. 19, 1917 
Dissemination of Angular Leaf spot of Cotton 
47i 
terial disease of peaches, etc., since the desiccation resulting killed the 
bacteria which had been spread. The physiology involved in our subject 
has not as yet been determined—whether negative heliotropism, positive 
chemotropism, or mere chance determines the time within which the 
bacteria enter the stomata—but it is true that infection resulted almost 
uniformly when the inoculation was made in direct sunshine on the upper 
or lower surface of the leaves with a temporary unprotected layer of water 
over the leaf surface. It may have been that a small percentage of these 
organisms withstood the unfavorable environment until night and that 
penetration of the leaf occurred then. The result of the author's experi¬ 
ments on the effect of sunlight upon Bacterium malvacearum agree with 
those of Rolfs (1915, a) and Edgerton (1912), in that the present writer 
found that 15 minutes' exposure kills some bacteria, 30 minutes a con¬ 
siderable number, and in an hour almost total destruction of the bacteria 
in the exposed parts of poured agar plates occurs. Some growth always 
appeared at the edge of the exposed area, and this was thought to be 
due to spreading from the margin of the shaded portion. More evidence 
on this point is needed. The conditions following rains seem to exert little 
influence on the spread of the angular leafspot of cotton. 
Stewart and Leonard (1915, 1916) show conclusively that sucking 
insects are capable of inoculating young pear trees with Bacillus amylo- 
vorus when the bacteria are present upon the twigs at the immediate 
point of puncture or upon the mouth parts of the insects. Flies, etc., also 
have been determined to be a probable means of spread of the bacteria. 
To what extent these agents work together, in what other ways the bac¬ 
teria may be spread from place to place to be inoculated by sucking 
insects, or to what extent inoculation may follow after insect punctures 
(since insect activity is lessened by rains, and the spread of the disease, 
according to these authors, is most noticeable after rainy periods) have 
not been determined. These authors state (1915, p. 121) that— 
On the other hand, it is to be noted that sucking bugs may be present in great 
numbers without the occurrence of much blight, 
then describe two situations differing only in the amount of rainfall, and 
conclude that the resistant condition of the trees in the case where the 
drought prevailed lessened the blight as compared to a severe outbreak 
in the case of an abundant rainfall. 
The work on Citrus canker is of particular interest and importance in 
this connection because the southeastern Citrus region is subjected to 
the tropical hurricanes, storms in which the wind blows highest and long¬ 
est during rainfall and which above all others would serve for this pur¬ 
pose. Hasse determined the pathogenicity of her organism without 
wounds or injuries of the host plant, and Wolf concludes that rain and 
dew must serve as agents of local dissemination. If the action of a hur¬ 
ricane be combined with the motility of such a bacterium, in view of 
