314 DISEASES OF ECONOMIC PLANTS 



lack of light, improper temperature, and especially by too 

 warm soil, and is readily controlled by careful management. 



Mosaic. — Upon the tomato appears a disease very 

 similar to the mosaic of tobacco. Aside from this ap- 

 parent kinship little is known about it. 



Rosette (Rhizoctonia sp.). — This rosette is possibly 

 identical with the potato rosette,^ showing similar lesions 

 upon the root and stem near the ground. The tops have 

 long internodes and dwarfed leaves which are somewhat 

 curled. For further discussion see potato. 



Upon the ripe fruits, especially those touching the ground, 

 this cUsease occurs as a brown rot upon a shghtly wrinkled 

 epidermis. 



TURNIP 



Black rot {Pseudomonas campestris (Pamm.) E. F. Smith). 

 — ^It was upon this crop in 1892 that the disease, now 

 known in so destructive a form upon the cabbage and 

 other cruciferous crops, was first noted by Pammel." It 

 then caused 10 per cent loss ; the next year 50 per cent, 

 and it has since been known to cause total ruin in many 

 instances. 



The rot is recognized by the blackened veins in the 

 crown, root, leaf stems, and leaves. The softer tissue 

 near such veins is abnormally watery, and the interior of 

 the root undergoes dry decay with a characteristic strong 

 odor. The cavities thus made are of peculiar radiate 

 form, with black or brown walls. Diseased plants may 

 live for considerable time with apparently healthy leaves, 



1 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 145, November, 1903. 

 « Pammel, L. H., la. Agr. Exp. Sta. Bui. 27, 1895. 



