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 which 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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