CHAPTER XI 

 THE GYMNOSPERMS 



THUS far we have devoted our time to the study of the 

 higher plants, that is to the plants which produce flowers and 

 seeds. This great group of trees, shrubs and herhs presents by 

 far the most conspicuous types of vegetation and includes our 

 most important agricultural crops. But we must now con- 

 sider the gymnosperms (for classification, see Chapter V), that 

 great group of seed-bearing plants which do not produce true 

 flowers. They are also called coniferous or cone-bearing plants 

 because of the cones which contain the seeds. The largest, most 

 important and best>known group is the order Pinacece which 

 are widely distributed throughout the world especially in the 

 northern hemisphere. They are the pines, spruces, firs, bal- 

 sams, larches, cypresses, cedars, hemlocks, arbor vitse and the 

 giant red oaks of our Pacific coast. 



Structure of Stems. The general character and gross struc- 

 ture of the stems and roots is somewhat similar to the angio- 

 sperms, but the leaves are modified until in most cases they are 

 described as needles. These needles may be compared to the 

 midrib of an ordinary leaf, but when cut in cross-section and 

 examined under the microscope they show a thick cuticle and 

 epidermis covering a few layers of sclerenchyma cells (Chapter 

 VIII), which in turn cover the chlorophyll bearing parenchyma 

 (Chapter VIII). . The small size and peculiar structure of the 

 leaves make them especially well suited for withstanding either 

 dry or cold climates. Most coniferous trees shed their needles 

 gradually and, therefore, are in foliage the entire year. For 

 this reason they are known as evergreens and are especially suit- 

 able for ornamental plantings. Some few conifers such as the 



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