406 



BOTANY. 



terns are well defined, and include most of the tissues de- 

 scribed in Chapter VI. (page 69 et seq.). 



The epidermal system consists of one or more layers of 

 epidermal cells, which are frequently much thickened; 



Fig. 301. Diagrammatic cross-sections of the stem of Gymnosperms. A, young- 

 stem with the flbro-vasciilar bundles, fb, widely separated ; p, the phloem ; x, the 

 xylem ; /*, tissues of the fundamental system ; e, epidermis. 5, a similar section of 

 an older stem, the cambium layer, o, extended through the fundamental system 

 from bundle to bundle. C, section of a three-year-old stem, showing the manner of 

 increase in the xylem and phloem ; pc, primary cortex (phloem) ; sc, secondary cor- 

 tex (phloem) ; c, cambium layer; tw, secondary wood (xylem); pw, primary wood 

 (xylem) ; p, pith ; pl,p2,p3, 1, a;2, tc3, corresponding phloem and xylem portions 

 of each year's growth of the bundle. 



stomata are common, and in general, are quite regularly dis- 

 posed in lines ; the outer surf ace is occasionally covered with 

 well-developed trichomes ; in general, however, they present 

 themselves as rough points, which give a harshness to the 



