90 



BACTERIA IN RELATION TO PLANT DISEASES. 



ECONOMIC ASPECTS. 



The economic aspects may be considered under four heads : ( i ) Losses ; 

 (2) Natural methods of infection ; (3) Conditions favoring the spread of the disease ; 



(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. To 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 b)- the pathologist him- 

 self, who will be better able than anyone else to note 

 down just those things likely to influence the host- 

 plants fa\-orably or unfavorabl}-. Some of these things 



Fig. 74.- 



*Fic. 74. — Bacterium Slcn'iirli (Erw. Sm.) attacking sweet corn (Zca mays). The section was 

 cut from the extreme upper part of a sceilhng leaf which was fi.xed in strong alcohol six days after 

 placing the hacteria 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 hacteria 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 C are three stomata. The substomatic chamber under A is free. B, with its 

 surroundings, is shown more highly magnified in fig. 75. Drawn with help of the Abbe camera. 



