390 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



The writer has since proved several diseases to be trans- 

 mitted by insects, notably the wilt of cucurbits, and here the 

 transmission is not purely accidental, but there appears to be 

 an adaptation, the striped beetle (Diabrotica vittata), chiefly 

 responsible for the spread of the disease, being fonder of the 

 diseased parts of the plant than of the healthy parts. This 

 acquired taste, for it must be that, works great harm to melons, 

 squashes, and cucumbers. Whether the organism winters 

 over in the beetles, as I suspect, remains to be determined. 

 Certainly the disease appears in bitten places on the leaves 

 very soon after the spring advent of the beetles. 



In 1897 I showed that molluscs sometimes transmit brown 

 rot of the cabbage, and last year I saw indications in Southern 

 France which lead me to think that snails are responsible for 

 the spread of the oleander tubercle, i. e., I saw them eating 

 both sound and tubercular leaves, and found young tubercles 

 developing in the eroded margins of bitten leaves. 



Parasitic nematodes break the root tissues and open the way 

 for the entrance of Bacterium S olanacearum into tobacco and 

 tomato, as was first observed by Hunger in Java and later by 

 myself in the United States. One of the serious problems of 

 plant pathology is how to control lleterodera radicicola, not 

 only because of its wide distribution on a great variety of 

 cultivated plants and the direct injury it works, but also on 

 account of the often very much greater injury it causes 

 through the introduction into the roots of the plant of bacterial 

 and fungous parasites. The man who shall discover an effect- 

 ive remedy will deserve a monument more enduring than 

 brass. Our Southern States in particular are overrun with 

 this parasite. 



Much remains to be done before we shall know to what ex- 

 tent fungous parasites function as carriers of parasitic bac- 

 teria. H. Marshall Ward sought to explain the presence of 

 bacteria in diseased plants by supposing that they must enter 

 the plant through the lumen of fungous hyphae. In this 

 lie was wrong, certainly if it be stated as a general proposi- 

 tion, but it appears to be clear that in some cases the two types 

 of parasites work together, the fungus invading first, and the 



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