18 PLANT DISEASES 



through carelessness in not promptly destroying by burning 

 diseased plants, fruits, bulbs, etc., which in most instances 

 can be readily done without much expense or loss of time. 

 For instance, it is not unusual to see quantities of diseased 

 leaves and fruit on the ground in orchards. If such are 

 allowed to remain, the fungi present continue to produce 

 spores, or winter-spores or sclerotia are formed; and al- 

 though the leaves and fruit ultimately decay and disappear, 

 the spores and sclerotia do not perish, but remain on the 

 ground until the following spring, when they give origin to 

 spores that are conveyed to the young leaves, and the 

 disease appears once more. Of course, the cultivator of 

 plants cannot directly prevent the diffusion of spores by 

 wind or other agents; but what he can do and what it 

 pays to do is, by systematic cleanliness and promptitude, 

 to prevent, to a very great extent, the formation of spores 

 on the plants over which he exercises control. 



Burn all diseased plants, fruit, and bulbs, and do not 

 throw them on the manure-heap, which means securing a 

 recurrence of the disease. 



It has been already explained that the majority of 

 parasitic fungi possess more than one form of fruit ; and 

 furthermore, the summer form of fruit is the one that pro- 

 duces a quickly spreading disease or epidemic, usually 

 appearing in late spring or early summer, and con- 

 tinuing to extend its ravages throughout the season, unless 

 checked. 



When a disease appears, remove the diseased plants, and 

 spray tlie remainder at intervals with solution of potassium 



