942 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Conclusion. 



As a general rule, it will be seen that only the wild plants most nearly 

 allied to the cultivated forms are likely to be infected by the same disease ; 

 but there are so many exceptions (e.g. Marrow and Hop Mildews) that 

 this cannot be taken for granted ; whilst in the case of heteroecious para- 

 sites, like the Pear-leaf Cluster-cup, the most unlikely plants are frequently 

 the culprits. 



In many of the cases mentioned it is comparatively easy to remove 

 the sources of infection, but in others it is more difficult, notably those of 

 fruit-trees. It will, however, generally be found that even in the latter 

 something may be done in the way of prevention ; and failure need not be 

 courted by innocently planting a crop in the neighbourhood of diseased 

 plants ; for instance, when planting choice varieties of Plums, one would 

 avoid Blackthorn as a neighbour. But when once the cultivator is alive 

 to the existence of such dangers, each one for himself will strive not only 

 to cure his diseased plants, but to exterminate other plants which may 

 be providing a nursery-ground for the mischievous germs. 



