On the Potato Disease 



197 



fungus. A fortnight later a second plant was removed from 

 the cool to the warm house and placed under a bell-jar. 

 Within a week of the removal of this plant, it also was 

 covered with Phytophthora. The third plant continued 

 growing in the cool house for thirteen weeks, and remained 

 perfectly free from obvious disease." 



There is another direction by which the same conclusion 



may be reached. Let any one who has a potato plot in which 



the disease is showing itself dig up some of the diseased 



plants and examine what remains of the " set." It is, perhaps, 



generally supposed that these sets (portions of underground 



stem, carrying buds) rot away after their buds have developed. 



This is not always the case. They are almost always eaten 



to some extent by larvae and sometimes they are destroyed 



by decay, but very often portions of them remain almost 



sound, and now and then almost the whole is still there 



and in a sufficiently vigorous condition to be attempting 



to put forth new buds. It is not difficult to decide whether 



these sets show signs of disease and in a certain number of 



cases these will be quite definite. Discolorations will be seen, 



exactly like those which occur in gathered tubers in autumn. 



The results from the writer's investigations in a potato garden 



at Haslemere have been to show that in some instances the set 



appears to be quite sound, whilst in some it is obviously 



diseased, and that in the latter the lower leaves are usually 



diseased and the topmost may be free. In very few instances 



did any of this year's tubers show the slightest trace of 



disease. 



It will, of course, be asked why, if the fungus be present 

 in the sets, it does not cause them to rot ? The answer to 

 this is a little difficult, but we may fall back on Massee's 

 experiments for conclusive proof that it does not always do 

 so. It may be suggested that in some instances the vital 

 endowments of the living tuber are sufficient to counteract the 

 activity of the parasite and that the latter can only assert its 

 power when the set is enfeebled by the production of its 

 progeny. This would be quite in accordance with much that 



