2 DISEASES OF FIELD & GAKDEN CROPS. [CH. 



are taken first, so that the simpler examples gradually 

 lead up to the more involved ones. 



The great question of the prevention, palliation, or cure 

 of plant diseases is, as a rule, almost entirely overlooked 

 by botanists ; but from a practical point of view, and these 

 notes are specially prepared for practical agriculturists, 

 the prevention, palliation, or cure of plant diseases should 

 surely be an object to be kept chiefly in view. 



A knowledge of the structure and vital phenomena of 

 field and garden plants should be used as a sure stepping- 

 stone to vegetable pathology. It must be confessed, 

 however, that in the same way as surgery is often more 

 precise and certain than medicine, so, much more is at 

 present known of vegetable physiology and anatomy than 

 the nature of disease and its prevention. We clearly 

 know the nature of some diseases of plants ; but as regards 

 the treatment of plants when invaded by parasites which 

 are too often the sole cause of disease, we frequently know 

 nothing. The reason for this defective information is 

 clear : there are no special teachers of vegetable pathology 

 in this country, and the few men who have made the 

 subject more or less a speciality, have not the time or 

 opportunity for extensive and continued experiment and 

 research. Field crops under disease are rarely or never 

 examined by competent observers. As nearly every 

 known disease of the animal kingdom is susceptible of 

 preventive, palliative, or curative treatment, it is only 

 reasonable to assume that the diseases peculiar to the 

 vegetable kingdom are also susceptible of similar manage- 

 ment. Of late years the spread of disease in the animal 

 kingdom has been greatly curtailed, and in the human 

 family the death-rate of towns has been much reduced. 

 These results have been entirely brought about by the 

 acquisition of an exact knowledge of the diseases peculiar 

 to animals, and of the circumstances favourable to the 

 spread or extinction of disease. Sanitary improvements 

 have considerably extended the average length of human 



