go BACTERIA IN RELATION TO PLANT DISEASES. 
ECONOMIC ASPECTS. 
The economic aspects may be considered under four heads: (1) Losses; 
(2) Natural methods of infection ; (3) Conditions favoring the spread of the disease ; 
sere 
EAS 
‘4 
Nae 
Fig. 74.* 
(4) Methods of prevention. 
In the United States Department of Agriculture 
and in our State Experiment Stations, naturally, much 
stress is laid on economic considerations, especially on 
2, 3, and 4. A knowledge of 2 and 3 will frequently 
lead to some simple and effective means of prevention. 
LOSSES. 
It is desirable that there should be made from time 
to time a careful estimate of the losses caused by each 
particular disease, not only as a warning to farmers, 
fruit-growers, market-gardeners, and florists of the exist- 
ence of these dangers, but also as an aid to legislatures 
and governments in deciding how much money may 
be judiciously appropriated for the scientific investiga- 
tion of these problems. Pathologists are urged to make 
and publish such records. It is perhaps unnecessary 
to add that the determinations should be reasonably 
accurate, otherwise it were much better not to make 
any records. Occasionally, when diseases are wide- 
spread and destructive, so that depreciation of land 
values and the hostility of a community might result 
from great publicity, the pathologist may have to con- 
sider discretion the better part of valor and refrain 
from publishing, but in this event he should not fail 
to make full records which may subsequently be pub- 
lished or at least consulted. What we need and must 
finally have is a large body of accurate statistics, 
covering a series of years, many localities, and many 
diseases. ‘Io make these statistics most useful, certain 
meteorological data should be collected in the same 
localities. ‘To be of most service this data concerning 
the weather should be recorded by the pathologist him- 
self, who will be better able than anyone else to note 
down just those things likely to influence the host- 
plants favorably or unfavorably. Some of these things 
*Fic. 74.—Bacterium Stewarti (Erw. Sm.) attacking sweet corn (Zea mays). The section was 
cut from the extreme upper part of a seedling leaf which was fixed in strong alcohol six days after 
placing the bacteria on its tip. At the time of inoculation water was extruding from the leaf-tip, as 
shown in fig. 73. This figure represents a longitudinal vertical cut. The dotted and heavily shaded 
parts show the location of the bacteria which have entered through the ordinary stomata and have 
not yet penetrated the vascular system, although in places, as at D, they are close to the spiral ves- 
sels. At A, B, and € are three stomata. The substomatic chamber under A is free. _B, swith its 
surroundings, is shown more highly magnified in fig. 75. Drawn with help of the Abbe camera. 
a 
