LIVER IVOR TS A XD MOSSES. 



57 



64. The leaves are also more highly developed than in 

 liverworts. They are always sessile and are arranged in two 

 (rarely), three, or more vortical ranks along the stem, 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 (frequently 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). 



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 likely to arise some 

 distance below the apex, so that the 

 stem is a succession of lateral 

 branches, called a sympodium (fig. 

 71). This mode of branching is 

 termed sympodial. In other cases 

 the main axis continues its growth 

 unchecked, and more or fewer 

 branches also develop. These lie 

 plainly upon the sides of a central 

 axis. This mode of branching is FlG 7I ._ Axis of a moss (Ortko . 



/-olUrl -nirMnhnrlinl Oft^n rVip trichniii) showing sympodial 



Called monOpOaial. tne branching. .S VV.ja, S,succes- 



,1 r .1 i i j c. si ve clusters of sexual organs, 



growth ot the lateral axes is den- p rodu ced at apex which check 



-.1 i- , j j ,1 j i the growth of axis. Beneath 



nitely limited and their develop- each" a lateral growing point 



i r develops, producing successively 



ment regular, forming a pinnate the b nces /-', ** ^. Magni- 



i i -rr .1 j rit-d 10 diam. Alter l'>nu-h A: 



branch-system. It the secondary schimpt-r. 



axes themselves branch, there is formed a bipinnate or 



even tripinnate system, as in figure 67, B. 



