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 croas-sectiona of the stem of Gymnoeperms, A, young 

 stem with the flDro-vascuIar himdlea, fb, widely separated ; p. the phloem ; aj, the 

 xylem ;/5, tissues of the fundamental system : e, epidermis, fi, a similar section of 

 an older stem, the <ambinm layer, c, extended through the fundamental system 

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

 increase in the xylcm and phlocim ; pc, primary cortex (phloiim) ; «c, secondary cor- 

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

 (xylem) ; p, pith ; pi, p2, p3, xl, mH, tcS, correepondiug phlogm aud xylem poniona 

 of each year a 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 -developed trichomes ; in general, however, they present 

 tliemselves as rough points, which give a harshness to the 



