BACTERIAL DISEASES OF PLANTS 89 



Exercise 129. The Wilt of Sweet Corn Caused by Pseudomonas Stewartii 



In some market-gardening sections this disease may be found, 

 but it is not widely distributed. It attacks only sweet corn, not 

 field corn nor pop corn. 



1. Note the wilted appearance of an affected plant. 



2. Make razor sections of stalks of diseased plants and examine 

 the fibrovascular bundles. Note the slimy yellow material wlxich 

 oozes from the fibrovascular bundles. Examine a drop of this 

 substance for bacteria. How would you explain the pathological 

 symptoms noted in the plants ? 



3. Make a study of the organism growing in gelatin stab, 

 agar slope, and potato. Make stains with carbol-fuchsin and 

 Gram's stain. 



Exercise 130. The Black Rot of Cabbage Caused by Bacillus campestris 



1. Examine cruciferous plants which may be affected, with 

 this disease. Notice particularly the effect on leaf and stem. 



2. Cut stems and leaf petioles transversely. Examine the fibro- 

 vascular bundles. Do the organisms ooze from the cut bundles ? 



3. Make razor or paraffin sections and examine minutely with 

 the microscope. What effect does the organism exert upon the 

 walls of fibrovascular elements ? 



4. Study the growth of the organism on gelatm stab, agar 

 slope, litmus milk, potato, and bouillon. Make stains with carbol- 

 fuchsin and Gram's stain. 



5. Inoculate young cabbage or turnip plants growing in the 

 greenhouse by puncturing their leaves with a needle bearing 

 bacteria taken from one of your cultures. JNIake notes and 

 sketches illustrating the progress of the disease. 



Exercise 131. The Soft Rot of Vegetables Caused by Bacillus carotovorus 



Jones. Thirteenth Kept. Vermont Agr. Exp. Sta., 1901. 



Potter. Centralbl. f. Bakt., 2te Abt., 7 : 282, 353. 1901. 



Jones, Harding, and Morse. Bulletin No. 147, Vermont Agr. Exp. Sta., 1910. 



1. Examine a carrot or other vegetable infected with the 

 organism in question. Note the size and shape of diseased areas. 



