232 DISEASES OF TROPICAL PLANTS OH . 



attacks the foliage, causing numerous circular, black, 

 velvety, slightly - raised spots, mostly on the lower 

 surface of the leaves, with correspondingly slight de- 

 pressions on the opposite surfaces. This disease is 

 more or less common in the Eastern Hemisphere, and 

 the same or a similar disease has been reported from 

 Dominica. 



Root Disease. This disease has been reported from 

 Barbadoes, Grenada, Dominica, St. Kitts, and Nevis, 

 but the data is so meagre that it is impossible to say 

 whether it is the same in all places. The diseased plants 

 lose colour, and shrink in some places. The loss from 

 this cause alone has been very great. The fungus causes 

 a cobweb growth of mycelium over the roots, resulting 

 in their death. It then spreads to the collar and the 

 stems. Thus far, no fruiting stage of the fungus has 

 been discovered, but after a time many small brown 

 spherical sclerotia about one mm. in diameter are 

 formed, and serve to perpetuate the pest. This 

 fungus has been reported on the aroids, antirrhinums, 

 and some composites of Barbadoes, on egg-plants, 

 tomatoes, and seedling limes in Dominica, and alfalfa 

 in Antigua. The diseased plants should be pulled and 

 burned, the land limed rather freely, and put in some 

 crop not subject to the disease for some time. The 

 seeds can be sterilized by soaking them in a solution of 

 corrosive sublimate (one part to 1000 parts of water) 

 for five minutes. 



CABBAGE AND RELATED PLANTS 



Club Root. This disease is due to Plasmodiophora 

 brassicae, Wor., and is widely spread throughout both 

 tropical and temperate regions. It is known under a 

 great many common names ; in Germany it is " Kohl- 

 hernie," in France it is " maladie digitoire," in Belgium 

 it is " Vingergiekt," in Russia it is " koponstnaga kila," 

 in Great Britain it is " Aubury," "Hamburg," and 

 "finger and toe," and in America it is "club foot," 



