FOLIAGE-LEAVES 



17 



single mid-rib, has several large main veins which radiate in 

 various directions from the base of the lamina towards its 

 margins — e.g. Mallow. 



Division of the Lamina. — The form of the lamina may be 

 very simple, because all the spaces between the nerves are com- 

 pletely occupied by leaf-substance — e.g. Pear, Hazel. Often, 

 however, incisions of considerable depth proceed from the 

 margin, thus tending to complicate the form of the lamina 

 and to split it into smaller sub-divisions. The degree to which 

 the leaf is divided into smaller parts varies ; for instance, the 

 incisions are shallow in the Oak-leaf, but they are deep in the 

 Buttercup-leaf. So long as the divisions do not reach the 

 large nerves, the leaf is said to be simple (figs. 19-22, 24-26). 



Figs, ig-23. — Division of pinnately- veined lamina. 



When the lamina is divided by incisions which reach the 

 main ribs there is no longer one single lamina, but there 

 exist a number of distinct leaflets, and the leaf is described 

 as compound (figs. 23, 27) — e.g. Rose, Pea (fig. 59), Clover. 



Figs. 24-27. — Division of palmately-veined lamina. 



Since a compound leaf consists of a number of distinct leaflets 

 attached to a common stalk, it may be asked why should we 

 not term it a branch and describe the leaflets as leaves. 

 Several reasons may be given which serve to show that a com- 

 pound leaf is a single leaf, and is not a branch. 



