48 



OUTLINES OF PLANT LIFE. 



amount of green tissue is increased by the formation of verti- 

 cal plates similar to the blade (fig. 44). 



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

 Sometimes the growth of the lateral branches, as of the 

 original main axis, is checked by the formation of sex organs. 

 In that case a new branch is likely to arise some distance 



Fig. 43. Fig. 44. 



Fig. 43. — A, leaf of a moss {Funaria Americana), showing central rib. Magnified 



about 40 diam.; B, upper portion of the same leaf, highly magnified, showing single 



layer of cells forming the blade and the narrower cells of the thick rib — After 



Sullivant. 

 Fig. 44. — Tip of leaf of a moss {^Oligotrickum aligerum^, showing the thickened 



rib, and the plate-like ridges on blade and rib greatly increasing the surface of 



nutritive tissue. Magnified about 75 diam, — After Sullivant. 



below the apex, so that the stem is merely a succession of 

 lateral branches (fig. 45). This mode of branching is called 

 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 called monopodial. Often the growth of the 

 lateral axes is definitely limited and their development regu- 

 lar, forming a pinnate branch-system. If the secondary axes 



