CHAPTER XTX 



SPERMATOPHYTES (Continued) 



Angiosperms (Seeds Enclosed) 



General Characteristics. — The Angiosperms are the most 

 highly evolved group of the plant kingdom, being the most per- 

 fectly adapted to terrestrial conditions. They also surpass all 

 other groups in economic importance, for they include the large 

 majority of our cultivated plants. Our dependence upon the 

 grains and fruits and upon forage, root, and tuber crops attests 

 the economic importance of the Angiosperms. The Angiosperms 

 probably have more species than any other group of plants and 

 show more variations. Approximately 125,000 species are 

 known. They form the most conspicuous part of our vegetation, 

 for not only most of our cultivated plants but nearly all weeds 

 are Angiosperms. The origin of the Angiosperms is not known, 

 but they probably arose from some Fern-like plants as the Gym- 

 nosperms did. The Angiosperms, as the name suggests, are 

 characterized by having their seeds enclosed. The enclosure is 

 the ovary, which is one of the notable features of Angiosperms. 

 Another notable feature is the flower, which is regarded as a 

 special type of strobilus. They also differ from the Gymno- 

 sperms in having more reduced gametophytes. Both male and 

 female gametophytes consist of only a few cells and have lost all 

 traces of sex organs. Since the gametophytes are microscopical, 

 most people are acquainted with only the sporophytes of Angio- 

 sperms. In character of roots, stems, leaves, flowers, seeds, and 

 fruits, there are numerous variations in Angiosperms, but, since 

 Part I of this book is devoted chiefly to these variations, the dis- 

 cussion will now be limited to the characteristic features of the 

 group and to such features as characterize the families of most 

 economic importance. 



The Flower. — -The flower (Fig. 407), consisting of a perianth 

 (calyx and corolla), stamens, and one or more pistils, is a structure 



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