EXPERIMENT STATION REPORTS. 268 



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capacity in foriiuilating the general plan of the work. In this latter 

 capacity I went to Pittsburg in January for a conference of all cooperat- 

 ing parties. 



In the prosecution of these investigations Mr. Doolittle has deter- 

 mined the infectious nature of the mosaic diseases of cucumber; show- 

 ing that it can be carried from a diseased plant to a healthy plant by 

 plant lice. The organism causing the disease has not been isolated as it 

 has not been possible to cultivate it so far. It is exceedingly minute, passing 

 through the ordinary bacterial filters, constituting thus a so-called 

 ''filterable virus." The disease is transmissible by aphids, or by hypo- 

 dermic injection of an extract of a diseased plant, from cucumber to 

 muskmelon and squash and vice versa. Further experiments on other 

 hosts are in progress, as well as experiments to determine the means of 

 Gver-vrintering. 



One of the most important pieces of work that can be undertaken is 

 the plant disease survey of Michigan. Up to the present the necessary 

 funds have been lacking, so that it has been impossible to make such a 

 survey in a systematic manner. However, it is possible to get an idea 

 of what are the more pressing plant diseases from the letters and other 

 inquiries that come to the College. Occasionally diseases new to the 

 State or even to science are brought to light through such correspond- 

 ence. It is greatly to be deplored that not all tlie correspondence on 

 plant disease topics and specimens of plant diseases sent in are turned 

 over to this department. At present at least two other departments 

 make it a practice to answer such letters and make no records and do 

 not preserve the specimens. These records and specimens would add 

 greatly to the completeness of our information on this subject. It 

 is furthermore regretable that such letters are not all referred to this 

 department since, through unfamiliarity with the current literature on 

 plant diseases on the part of those departments, the diagnoses made 

 and the control measures advocated are not in all cases entirely trust- 

 worthy and often are at variance with the findings and recommendations 

 of this department. 



It must be conceded that these departments had in the past an ex- 

 cellent reason for occupying this field in view of the fact that plant 

 pathology was not in the hands of a trained pathologist in this de- 

 partment, but that time has long passed and efficiency and accuracy 

 would seem to require that all letters and inquiries even of the simplest 

 nature, on plant diseases be referred to this department. This should 

 be viewed by these other departments as a measure of protection to them 

 as it is obvious that they will thus be relieved from the danger of making 

 false diagnoses. 



It w^ould seem highly desirable to establish a plant survey project in 

 this department either in the Experiment Station alone or in coopera- 

 tion with the Extension Division. The object of such a project would 

 be ''To give instruction and" practical demonstration in the identifica- 

 tion and control of plant diseases, including advice through correspond- 

 ence and personal visits to farms and orchards, in cooperation with 

 county agents, farmers' organizations, and individuals." Special at- 

 tention would be given to certain of the more important crops. In the 

 course of this work correspondence would be followed up by personal 



