POTATO DISEASE. 287 



This scheme is not proposed with any idea of discovering 

 a certain and infallible cure for the disease. The experiments, 

 as I have already remarked, must be expected to lead only to 

 an approximation to the desirable end, but at the same time to 

 open the way to the discovery of many valuable facts that bear 

 relation to the general diseases of plants, tending thereby to 

 promote one of the least known and most useful branches 

 of agricultural science. In accordance with the preceding 

 views, I present the following synopsis of a plan upon which a 

 series of experiments might be based: — 



I. The first series might be designed to ascertain whether the 

 disease be contagious or non-contagious. If contagious, it may 

 be communicated by planting the tuber in a soil in which a 

 diseased crop was raised on the preceding year. It may also 

 be communicated by the use of compost in which some of the 

 affected tubers have been mixed. In order to ascertain whether 

 this hypothesis be correct, we should institute the following 

 tests. 



Let a field, containing half an acre of virgin soil, be prepared 

 and divided into two equal sections, taking care that the soil of 

 the whole field be uniform and equally exposed to light and 

 moisture. Fertilize one of the*se sections with a material 

 containing a large mixture of diseased potatoes reduced to 

 compost. Let the second be fertilized with a similar compost, 

 except that it shall contain no diseased potatoes, nor any 

 substance that is affected with the virus. Plant each section 

 with sound potatoes of the same variety and from the same lot, 

 after washing all the seed in some disinfecting fluid, to remove 

 any virUS that may exist on the surface of the tubers. Take 

 pains to cut open every tuber before planting it, to see that it 

 contain no visible marks of the disease, and reject all that do 

 not appear to be sound. 



If the crop in the first section, which was manured with a 

 compost containing virus, be evidently more diseased than the 

 crop in the other section, we have some presumptive evidence 

 that the disease is contagious. A few repetitions of the same 

 experiment, with invariably similar results, would establish the 

 point beyond doubt. But it would still remain to be proved 

 that there are not many other ways by which the disease might 



