8 THE PRINCIPLES OF AGRICULTURB 



fundamental importance to the farmer. From 

 the farmer's standpoint, there are four great 

 departments of plant -knowledge : physiology, or 

 a knowledge of the way in which the plant lives, 

 grows, and multiplies ; pathologj^ or a knowl- 

 edge of mal- nutrition and diseases ; systematic 

 botany, or a knowledge of the kinds of plants ; 

 ecology, or a knowledge of the inter-relations 

 between plants and their environments (or sur- 

 roundings), and how they are modified by 

 changes in environments, by crossing, and by 

 breeding. 



17. Animal-knowledge, or zoology. There are 

 also four general directions in which animal- 

 knowledge appeals to the farmer ; physiology, 

 with its practical applications of feeding, hous- 

 ing, and general care of animals ; pathology, or 

 knowledge of mal -nutrition and diseases (with 

 special applications in the practice of surgery 

 and medicine) ; kinds of animals, and the life- 

 histories of those which are particularly bene- 

 ficial or injurious to agriculture (with special 

 applications in economic entomology and eco- 

 nomic ornithology) ; ecology and breeding. 



18. Chemistry. There are two general direc- 

 tions in which chemistry appeals to the agn- 

 culturist : in enlarging his knowledge of the 

 life-processes of plants and animals ; and in 

 affording direct information of the composition 



