CHAPTER XII 

 INTRODUCTION 



Aside from some references to Gymnosperms, and to Yeast, 

 Bacteria, and a few other simple plants, Part I is devoted almost 

 entirely to a study of the Morphology and Physiology of the Flow- 

 ering Plants. The Flowering Plants deserve more attention than 

 other groups, because they are the most highly developed, most 

 attractive, and are the chief source of food, fibers, and many other 

 products related to the welfare of mankind. But in addition to 

 the Flowering Plants, the Plant Kingdom also includes many 

 kinds of plants which do not have flowers. In fact, not much 

 more than half of the 233,000 or more species of known plants are 

 Flowering Plants. About us are many kinds of plants w^hich do 

 not have flowers and some of them are also of much economic 

 importance. The Gymnosperms, the group to which Pines, 

 Spruces, Firs, and some other trees valuable for timber belong, do 

 not have true flowers but have seeds, and are almost as highly 

 developed as the Flowering Plants. The Flowering Plants and 

 Gymnosperms constitute the group called Seed Plants. But 

 there are many kinds of plants, which are often referred to as the 

 simpler plants, that do not even have seeds and some of these are 

 of much economic importance. Well known among the simpler 

 plants are the Ferns, Mosses, Algae, Fungi, and Bacteria. Both 

 the Fungi and the Bacteria are important economic groups. 

 The Fungi cause most of the plant diseases and consequently 

 much destruction and loss among cultivated plants. Many of 

 the Bacteria are indispensable to Agriculture, for they decompose 

 organic compounds, increase the nitrogen of the soil, and do other 

 things that are related to the soil fertility. On the other hand, 

 the Bacteria cause most of the animal diseases and these forms 

 we have to combat. 



Some of the simpler forms, like the Bacteria and many Algae, 

 are unicellular plants and hence are extremely simple, while some, 

 as the Ferns illustrate, have complex plant bodies and are com- 



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