LI\-ER\VORTS AXD MO.SSE.S. 



57 



64. The leaves are also more highly de\eloped than in 

 liverworts. Thev are alwaj's sessiie and are arranged in two 

 (rarely), three, or more \ertical ranks along the btem, and 

 consist usually of a single sheet of chlorophyll-bearing cells, 

 the blade (figs. 69, 70), and a central rib running from base 

 to apex (frec}uently wanting), which is composed of elongated 

 conducting and strengthening cells (figs. 69, 70). In some 

 the amount of green tissue is increased by the formation of 

 vertical plates similar to the blade (fig. 70 j. ■ 



65. Branching. — The stem branches, often very profusely, 

 by the formation of lateral growing! 

 points beneath the developing leaves. 

 Sometimes the growth of the lateral 

 branches, as of the original main 

 axis, is checked by the formation 

 of sexual organs. In that case a 

 new branch is likeh' to arise some 

 distance below the apex, so that the 

 stem is a succession of lateral 

 branches, called a sympodmm (fig. 

 71). This mode of branching is 

 termed sympodial. In other cases 

 the main axis continues its growth 

 imchecked, and more or fewer 

 branches also develop. These lie 

 plainlv upon the sides of a central 

 axis. This mode of branching is F,(;^,.„Axis of a moss fCrMo- 



111 i J- } /~\r^ -^ ,-1-. - trichum 1 showine svmpodial 



called monopndial. Otten the branching. 5', .s■^ .?=, v.succes- 



, r ^ ^ ^ ^ ■ J c sive clusters of se.xual orsans. 



growth ot the lateral axes is deh- produced at apex «-hich check 



, , . . , J ._L ■ J 1 the growth of axis. Beneath 



nitely limited and their develop- each a lateral growm? point 



1 ,- ■ ■ ^ develops, produciue successively 



ment regular, tormmg a pinnate the brances /.i, fk *=. Magni- 



1 , T,- ^1 J tied 10 diam. — .\fter Eruch & 



branch-system. It the secondary schimper. 



axes themselves branch, there is formed a bipinnate or 



even tripinnate system, as in figure 67, B, 



