xv STRUGGLE WITH DISEASE 183 



have been studying all sorts of little problems 

 which at first sight do not seem to have any 

 practical use at all, but which give them a know- 

 ledge of the conditions of life of plants which they 

 could not get in any other way. They have, 

 therefore, a starting-point from which they can 

 proceed at once to study the new problem of the 

 disease. 



In order to understand just what the struggle 

 with disease means, we shall take one case in a 

 little detail, that of the mildew or blight of wheat. 



This disease, to which the names of rust, mildew, 

 and blight are all given, is very old, for it was known 

 to the ancient Greeks, who had observed its ravages 

 in their corn-fields. They thought the cause was 

 the anger of the gods, and accepted it as one of the 

 inevitable evils of life. Similarly, the Romans were 

 quite familiar with the disease, which they thought 

 was due to a particular goddess, to whom they 

 offered sacrifices in order to avert her unwelcome 

 attentions from their crops. 



Pliny, some of whose curious opinions we have 

 already considered, speaks a good deal of mildew, 

 and what he says is very interesting. He begins 

 by saying that it is due to " the inclemency of the 

 weather," and goes on to say that " it attacks corn 

 most frequently in localities which are exposed to 

 dews, and in valleys which have not a thorough 



