472 
Journal of Agricultural Research 
Vol. VIII, No. 13 
the writer's results, this disease would undoubtedly be spread rapidly, as 
is noted by Stevens (1914). 
The application of these conclusions to other diseases of such plants 
as walnut, cabbage, curcubits, oats, clover, sugar cane, and sweet corn, 
caused by motile bacteria which infect the aerial portions of the host, 
I depends solely upon the prevalence of these meteorological conditions— 
that is, sufficient wind during rain to blow the water from plant to 
plant. It need not be from host to host, because other plants may serve 
as “ stepping stones,” as it were, provided the bacteria reached their 
host before the suspension became too dilute for infection. Their appli¬ 
cation is not at all limited to bacterial diseases, since there are many 
fungi, parasitic upon plants, having spores in sori, such as the Glomerellas 
and rusts, others having spores in pycnidia and in asci, where water is a 
necessary factor in their dissemination, and others having aerial spores, 
such as the Monilias and downy-mildews, where water is not necessary, 
yet in all probability would greatly augment infection by spreading the 
spores in the most favorable environment. 
It is this factor which places all of these diseases in one theoretical 
class as regards control. Fungicides have not been generally accepted 
as a logical means of preventing bacterial diseases, though their effi¬ 
ciency should be the same as in the cases of potato-mildew, apple-scab, 
etc. A protective compound applied to the susceptible parts, active in 
the presence of water and of sufficient toxicity to kill the several bacteria 
quickly, would be expected to have the same result as in cases where 
sprays are recommended. In fact, Rolfs (1915, a) reports successful results 
with Bordeaux mixture in the prevention of thisdisease. Stewart (1913, a) 
mentions certain unpublished observations by Reddick in which a spray 
on the blossoms of pear lessened fireblight. Wolf and Massey (1914, 
p. 100), referring to Citrus canker, state: 
Very encouraging indications of successful control have been obtained by the use 
of each of these fungicides [Bordeaux mixture, ammoniacal copper carbonate, and 
soluble sulphur]. 
Sprays have been tried by some one or another in the case of almost 
every bacterial disease, and in the majority of instances negative results 
have been reported. This has developed the more or less current opinion 
that the theory of such methods is incorrect; whereas from these data 
one might conclude that the theory is correct, improper fungicides or 
ill-timed applications having been the cause of failures. 
CONCLUSIONS 
In conclusion and by way of summary the following points may be 
reiterated as of greatest importance: 
(1) The methods of dissemination of many plant diseases, especially 
those caused by bacteria, are not satisfactorily described in the literature. 
