INTBODUCTOBY VIEW 7 



includes all of the seed-producing plants. To this group 

 belong almost all of the cultivated plants, and it is by far 

 the most important division in its relation to mankind. 

 The Thallophytes, however, are of considerable impor- 

 tance to man in that within its membership are to be 

 found the bacteria, both useful and harmful, and also the 

 numerous plant diseases. The farmer, therefore, is eco- 

 nomically interested chiefly in only two of the great 

 divisions of the vegetable kingdom, the Thallophytes and 

 the Spermatophytes. 



The two classes of Spermatophytes are the Gymno- 

 sperms and the Angiosperms. The Gymnosperms include 

 those plants the seeds of which are naked or not inclosed, 

 and are formed on the outside of a modified leaf. A 

 large number of the Gymnosperms are coniferous or cone- 

 bearing trees, such as the pine, cedars, yews, and similar 

 plants. The Angiosperms include those plants whose 

 seeds are inclosed in pod- or sac-like structures. To this 

 group belong almost all of the cultivated plants. The 

 Angiosperms may be divided into two sub-classes, namely, 

 the Dicotyledons and the Monocotyledons. The dicoty- 

 ledonous plants may be distinguished by the presence 

 of two cotyledons or seed leaves, while the monocoty- 

 ledons have but one. Both dicotyledonous and monocoty- 

 ledonous plants are to be found in our cultivated forms. 

 The Leguminosse, to which belong the clovers, peas, and 

 beans, is an example of the former, while the Graminese, 

 or grass family, to which belong the grasses and grains, is 

 an example of the latter. 



9. Length of life. — Based upon their length of life, 

 plants may be divided into annuals, biennials, and peren- 

 nials. An annual is one that lives only during one growing 

 season. A biennial is one that requires two growing 



