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 

 etem with the flbro-vascular bundles, /*, widely separated ; p, the phlogm ; as, the 

 xylem ; /«, tissues of the fundamental system : e, epidermis. B, a similar section of 

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

 from bundle to bundle. (7, section of a three-year-old stem, showing the manner of 

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

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

 <xylem) ; p, pith ; p\, p2, pa, xl, x2, (c3, corresponding phloSm aud 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 surface is occasionally covered with 

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

 tliemselves as rough points, which give a harshness to the 



