I.] INTRODUCTORY. 



life.. It is therefore only reasonable to believe that when 

 we completely understand the nature of plant diseases, and 

 the circumstances which aid their spread or tend to their 

 curtailment, we shall be more or less able to cope with them 

 by rendering surrounding circumstances unfavourable for 

 their extension. In the majority of instances it is almost 

 futile to expect cures : the knowledge to be sought for 

 must be the facts which will indicate some mode of pre- 

 vention, or some method of detecting and treating disease 

 in its earliest stages. In the same way as dwellers in 

 towns have been of late aroused from their apathy and 

 made to understand something of what is necessary for 

 health, so all agriculturists should, if possible, arouse 

 themselves and learn something of the nature and sur- 

 roundings of plant diseases. Till this knowledge is 

 acquired, and till agriculturists become alive to the pos- 

 sibility of saving their crops from disease, little progress 

 can be hoped for. We do not say that it is necessary for 

 every farmer to be a complete master of the anatomy and 

 physiology of all the plants he grows, or to be perfectly 

 familiar with the life history of every assailing parasitic 

 fungus or destructive animal, any more than a house- 

 holder should know all about the exact nature of typhus, 

 or diphtheria, or bacteria, bacilli, and disease germs ; but 

 as every householder at length begins to know, amongst 

 other facts, that an open drain is likely to prove fatal 

 to life, so every farmer should know, amongst other things, 

 that imperfectly-drained fields and rotting vegetable-refuse 

 mean disease and destruction to his crops. 



No sane healthy person would remain in a place tainted 

 with the contagia of dead and diseased animals, and it is 

 equally unsafe to place sound plants, tubers, or seeds, 

 amongst dead or diseased vegetable-refuse. In one case, 

 as in the other, certain individuals may perchance escape ; 

 but the general result is, the healthy organisms are at 

 length destroyed by the dead or diseased ones.. 



In regard to the illustrations prepared for this work, 



