EXPERIMENT STATION BULLETINS. 633 



THE HOST. 



The common commercial type of tomato is Lycopersicon ly coper sicon 

 (L.) Karst., aud is to be distinguislied from the currant tomato, Lycop- 

 ersicon pimpinellifolium Dunal, and the cherry tomato, Lycopersicon 

 cerasiforme Dunal. 



The importance of the tomato crop in the United States is indicated 

 by the following statement from the Thirteenth Census Report : ''Judged 

 by value, tomatoes were the most important vegetable, the value ex- 

 ceeding 113,700,000 in 1909." The Michigan tomato crop is extremely valu- 

 able. The report credits the state with |217,256, tomato production, and 

 this has since increased to at least five times this amount. 



The methods used in growing this crop influence the prevalence of this 

 disease to a great extent. 



Seed is sown in hot beds or greenhouses several weeks before setting 

 out; (in Michigan from March to May). In the open, two types of cul- 

 ture are employed: (1) training of plants to two or three stems tied to 

 a stake, (2) allowing plants to grow over the ground at will. In forc- 

 ing tomatoes, the plants are usually trained to a single stem and staked. 



In recent years more and more complaints, indicating the prevalence 

 of serious tomato diseases, have come from the tomato growers of Mich- 

 igan. The plant disease survey of the state indicated that Septoria leaf- 

 spot was especially serious. Investigation was begun by the writer in 

 September, 1913, and practically completed August, 1914. 



THE DISEASE. 



The common names by which this serious disease is known are: "late 

 blight," "blight," and "leaf-spot." It is, however, a well known fact 

 that in some sections of the country, tomatoes are attacked by Phytoph- 

 tJiora infestans (Mont.) de By., the cause of late blight of potato. This 

 precludes the use of "late blight" as a name for this disease. "Blight" 

 and "leaf-spot" are also more or less preempted. The former of these 

 terms or preferably "early blight" may best be associated with Alter- 

 naria solani (E. and M.) J. and G. which also attacks tomatoes. A com- 

 mon usage among pathologists seems to warrant the name of "leaf-spot" 

 in referring to the diseases of this type. 



PREVIOUS INVESTIGATION OP THE DISEASE AND ITS CAUSAL ORGANISM. 



It is generally conceded that the fungus, Septoria lycopersici Speg. 

 causes the disease commonly known as "leaf-spot" of tomato. As will 

 be seen this has been more of an inference based upon the constant asso 



