12 TRANSACTIONS OF THE [Sess. lxxvi. 



The remedy recommended is to remove whichever of the 

 host plants is considered to be of the least economic value. 



There exist among cultivated plants different varieties, 

 some of them predisposed to disease, others immune. The 

 immunity may be due to anatomical or physiological 

 differences. Whatever the cause of the immunity may be, 

 we can always test whether it exists or not by experi- 

 mental methods. The fact of great importance is that it 

 is possible to produce varieties which can resist certain 

 diseases, and we are now learning more about the laws 

 which govern the production of varieties, so that the special 

 variety desired can be produced with greater certainty and 

 rapidity than was formerly the case. Our future efforts in 

 stamping out disease must be concentrated more on the rear- 

 ing of resistant varieties than has been the case in the past, 

 and this is another of the ways in which the modern science 

 of Genetics will prove of great value in applied botany. 



The remedies for plant disease are mostly all of the 

 nature of antiseptics or fungicides. They are not of the 

 nature of medicines, as generally understood in animal 

 ailments. Still, much may be done by keeping the plant 

 healthy, and supplying it with the right kind and amount 

 of food. Attention to the proper supply of water, heat, 

 and light is also of importance. In other words, keep the 

 plant in a proper hygienic condition, and it will, like the 

 animal under similar conditions, be better able to resist all 

 kinds of disease. In order to do this we must study and 

 understand the inter-relationship between the plant and its 

 surroundings, and it is in this connection that the study of 

 plant (ecology from a physiological point of view is of such 

 vital importance. 



The method of dealing with outbreaks of disease when 

 they occur locally may be of advantage locally, but in- 

 dividual or isolated action, though of use, is of very little- 

 avail in stamping out an existing or preventing a threatened 

 epidemic, because the methods employed are not funda- 

 mental : they do not strike at the root of the disease. 



In stamping out disease we must have properly organised 

 and combined action, otherwise the best efforts are bound 

 in the long-run to prove futile. 



The Americans were among the first to realise the im- 



