THE SPREAD OF PLANT DISEASES. 129 



mined by it, and knoAV of fertile tracts miles in extent where 

 melon culture has been abandoned. When the soil is once infested 

 it is worthless for melon growing for a long time — five to seven 

 years, according to South Georgia growers who have had much 

 experience with it. 



A successful Sea Island cotton grower writes that he has 

 abandoned fifteen acres of his best cotton land on account of this 

 blight. A New York cabbage grower informs me that his best 

 soil, which formerly yielded abundant crops, is now worthless for 

 cabbage growing, and I know from a careful examination that his 

 sole trouble arises from the fact that his soil is infested with a 

 parasitic Fusarium. Undoubtedly these troubles have arisen, 

 or at least have become intensified, by too frec^uent growing of 

 the same croj), and the V)est remedy is to be found in a wide rota- 

 tion. At present I know of no other. 



Spread by Way of Seeds, Seedlijs(;s, Buds, Tubers, Cut- 

 tings, AND NuRSEKY'' Stock. — One of the best examples of a 

 disease disseminated on seeds is the loose smut of oats and 

 wheat. The smut spores simply adhere to the sound kernels, 

 germinate at the same time as the kernels, and bore into the young 

 seedlings, to remain hidden till the plants blossom. The parasite 

 of beet burn finds its way to the young seedlings in much the 

 same way, being carried to the beet fields along with the seed. 

 Potato scab is spread in much the same way, i.e., from the mother 

 tuber to the progeny, but this parasite also lives over in the soil. 

 A bad lettuce Septoria, which sometimes causes much trouble, 

 appears to be carried over from year to year, and spread from 

 place to place in the seed. 



Many diseases are distributed in seedlings, bulbs, buds, and 

 cuttings, and too much care cannot be exercised in their selec- 

 tion. Among these may be mentioned the Easter lily disease, the 

 yellow disease of hyacinths, certain violet diseases, the California 

 vine disease, peach yellows, peach rosette, peach mildew, and 

 peach curl.' 



But perhaps the most wholesale manner of distribution is 

 til rough the medium of irresponsible nurserymen. In this way 

 all sorts of fungi and insect pests are spread from one end of the 



1 Since this was written I have found that the bacterial brown rot or black rot of the 

 cabbage is often transplanted to healthy fields from the seed bed along with the young 

 plants. (See " Farmers' Bulletin," No. 68, U.S. Department of Agriculture, for a full ac- 

 count of this discovery.) 



