Apr. 29, igis A.ntkracnose of Lettuce 271 



ness of the leaves and not the splashing that was responsible for the spread 

 of the disease in this case. Undoubtedly a wet leaf is a more suitable 

 medium for most spores than a dry one, but the wetness of the leaf is of 

 no avail when the mechanism for bringing a spore to it is lacking. It 

 may be mentioned here that in greenhouses, where water drips upon 

 diseased and healthy plants, it has been observed that the plants in the 

 vicinity of the diseased plant become infected, owing to the splashing 

 of drops of water containing spores from diseased to healthy leaves. 

 When water drips on healthy plants alone, the leaves are equally wet, 

 but no infection occurs, indicating that wetness of the leaves alone is 

 not responsible. It is clear that the splashing of water contributes quite 

 largely to the spread of the pathogene in the greenhouse, and probably 

 rain is responsible to a large extent for its spread in the fields. The rela- 

 tion of this to the control of the disease will be considered later. 



NAME OF THE PATHOGENE 



The organism seems to be properly placed among the Melanconiales. 

 In America the fungus is commonly called "Mari-^oma /?er/oraw5'." The 

 description of this organism fits very well the Michigan specimens. How- 

 ever, Berlese (2) described what is undoubtedly the same organism several 

 months previous to the American description. Accordingly the specific 

 name " panattoniana" has priority. This was recognized by Appel and 

 Laibach (/) who retained the name "Marssonia panattoniana." 



Mangus (7) has shown that the genus Marssonia (sometimes erroneously 

 spelled "Marsonia") was given in 1861 by Karsten to a Phanerogamic 

 genus. This antedates Marssonia Fischer as a genus of fungi by 1 3 years. 

 Magnus accordingly has proposed the name "Marssonina" for the pre- 

 empted genus, and has made the new combination Marssoniyia panatto- 

 niana (Berlese) Magnus. 



The synonyms of this fungus are as follows : 



Marssonina panattoniana (Berlese) Magnus 



Marsonia panattoniana Berlese, 1895, in Riv. Pat. Veg., v. 3, no. 5/12, p. 34a 

 Marsonia perforans Ell. and Ev., 1896, in Ohio Agr. Exp. Sta. Bui. 73, p. 225. 

 Didymaria perforans (Ell. and Ev.) Dandeno, 1906, in 8th Rpt. Mich. Acad. Sci., p. 47. 

 Marssonina panattoniana Magnus, 1906, in Hedivigia, Bd. 45, Heft 2, p. 88-91. 



MORPHOLOGY OF THE CAUSAL ORGANISM 

 The fungus which causes the anthracnose of lettuce is a typical member 

 of the order Melanconiales. The mycehum of the fungus is composed of 

 slender, hyalin septate threads which penetrate between the cells of the 

 host. This mycelium is very scanty within the diseased spots except as 

 it becomes matted to form a fruiting layer. This fruiting layer is formed 

 beneath and upon the epidermis at a lesion. The fruiting layer is much 

 more diffuse than that of Gloeosporium or Colletotrichum. For this rea- 

 son Dandeno (4) has suggested that the fungus is in reality a species of 

 Didymaria. 



