MICHIGAN ACADEMY OF SCIENCE. 129 



ci'ganisiii was round, ((cciined in great abimdauce in a greenliouse 

 iu whieii couditions" were more moist tliau normal. This disease 

 showed up by causing blackish or at times slightly reddish elongated 

 lesions on the under side of the lower leaves, especially those rest- 

 ing on the ground. In the early stages the lesions were unevenly 

 sunken and at this time the color was mottled. In the later stages a 

 slightly i)inkish or buff colored, film-like mold api)eared on the 

 di.seased spot. This upon microscopic examination was found to be 

 composed of the basidia of Hjjpochnus (Corticiuin in the sense of 

 Burt.) "The lesions themselves contained an abundance of the typi- 

 cal threads of Ehizoctouia, but the deep color was not evident. 



Secondary rots frequently occurred and iu some cases large 

 masses of bacterial slime oozed out of the rotted stem. On the 

 withered leaf blades, a gray mold was common. As a result of 

 the combined action of these rot-producing forms, the entire petiole 

 was rotted off and left only a blackened patch upon the main stalk. 



Although work of a decisive nature has not been done with this 

 disease, in view of the well-known effects of Khizoctonia upon a 

 wide range of hosts, it seems safe to attribute this disease to some 

 species of Rhizoctonia. 



Lettuce Rosette. Another disease of lettuce has been associated 

 with Rhizoctonia by Selby.** This is the Lettuce Rosette. In this 

 disease the lesions instead of occurring upon the leaf petioles occur 

 upon the stems and roots as typical Rhizoctonia lesions, which 

 eventually cause a girdling and the associated rosette appearance 

 of the tops. 



No such appearance of stems or roots has been found, but on 

 the contrary, a rosette without any lesions and with complete 

 absence of Rhizoctonia threads has been found. This disease which 

 is found first in the seed bed, where naturally it can not be readily 

 seen, becomes prominent after the last transplanting. Affected 

 plants do not grow to any great extent after transplanting. The 

 few center leaves which are put out remain small and stunted and 

 present a marked contrast to the few outer leaves. In the last 

 stages the inner leaves die and blacken. 



This disease shows the vascular system in the roots markedly 

 discolored. Sections show the water tubes to be plugged by bac- 

 teria. Cultures, however, have not yielded any one germ with regu- 

 larity. The cause of this disease is as yet in doubt although it 

 seems that this is a bacterial disease of the same type as the celery 

 disease described earlier in this report. 



•♦Selby, A. D. -Ohio Sta. Bui. 145: 15-28. 1903. 4 figs. 

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