CHAPTER II 



THE STRUCTURE AND FUNCTIONS OF PLANTS 



BEFORE taking up a study of the diseases of plants, it 

 will be necessary to know something about the plant 

 kingdom as a whole, and more especially about the 

 fungi which are the cause of the great majority of plant 

 diseases. For this reason, the first part of this book is 

 devoted to a general discussion of the higher plants, 

 with which we are most interested in agriculture ; and 

 to a discussion of the systematic arrangement, the 

 morphological character, the physiology, and the methods 

 of reproduction of the fungi and other organisms which 

 cause disease. The second part is de\ 7 oted to a discus- 

 sion of the diseases of the most important crops, and 

 methods for prevention and cure of these diseases. 



The term "plant" as generally used refers to the 

 higher or seed-producing plants, and comparatively few 

 persons take into consideration the great number of 

 plants which do not produce seeds and which differ 

 materially in character and habit from the higher plants. 

 This is not because the seed plants are more numerous, 

 although in general they may be said to be more con- 

 spicuous than the plants which do not produce seeds ; 

 but because they are the plants on which mankind is 

 dependent in a great measure for food, clothing, fuel, 

 and building material. 



However, there is an enormous number of plants 

 which do not produce seeds, but reproduce by the 

 formation of very small bodies known as spores. Many 

 of these plants are extremely small and insignificant, 



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