262 Journal of Agricultural Research voi. xm, no. s 



portant. The general effects of these troubles may be contrasted with 

 the anthracnose. Aside from the insect and nematode depredations, 

 we have in general two types of injury to the mature plants; diseases 

 which rot the plants more or less, and those which disfigure the leaves. 

 In the first group may be mentioned drop, caused by Sclerotinia lihertiana, 

 and graymold, caused by Botrytis sp. Occasionally the softrot caused 

 by Bacillus carotovorus causes damage. Frequently lesions are found 

 in the petioles and blade which lead to the rotting off of the other leaves 

 of the plant. This disease is called "black stemrot," or "bottom-rot," 

 and species of Rhizoctonia have been found associated with this trouble. 

 Of the leaf diseases, the downy-mildew, caused by Bremia lactiica, 

 and the anthracnose are the most important. The efifects of B. lactuca 

 are such as would be expected from one of the downy-mildews. Light- 

 colored areas are noted on the upper surface of the leaves, while the 

 lower surface shows the conspicuous tufts of conidiospores of the organ- 

 ism. With young plants a drying up of the leaves may occur. 



COMMON NAME OF THE DISEASE 



In the previous accounts of this disease (j),^ several common names 

 have been used: "anthracnose," "shothole," "leaf -perforation," and 

 "rust." In Michigan greenhouses the name "rust" is probably most 

 common. The causal organism, however, has no connection with the 

 true rusts of plants. Hence, this name, though fairly descriptive and 

 popular, is, according to the prevailing usage among pathologists, not 

 to be recommended. The names "shothole" and " leaf -perforation," 

 while very appropriate, in so far as the lesions on the leaf blade are con- 

 cerned, do not properly consider the effect on the midrib, which is by 

 far the more disfiguring phase of the trouble. The name least open to 

 objection, and the one which is in accord with the best usage among 

 plant pathologists, is "anthracnose." This term has become a common 

 word among growers of other crops affected by similar parasitic diseases, 

 and will no doubt be readily accepted by greenhouse men. 



PREVIOUS INVESTIGATIONS 



The first account of the anthracnose of lettuce and the associated 

 organism was given by Berlese (2) in 1895. This writer, in a short note 

 after a description of the signs of the malady, named the associated 

 organism " Marssonia panattoniana." As will be seen in the discussion 

 of the etiology of this disease, Berlese recognized the parasitic nature of 

 the fungus, but did not make conclusive inoculation experiments. 



At almost the same time Selby (8, p. 224) published a brief note in 

 which he described the appearance of the affected plants. The asso- 

 ciated fungus was named Marssonia perjorans E. and B., Ellis and Ever- 



1 Reference is made by nmnber (italic) to "Literature dted," p. 280. 



