156 



PRACTICAL COURSE IN BOTANY 



Fig. 208. — Palmately net- 

 veined leaf of wild ginger. 



leaf (Fig. 208) into a number of primary veins or ribs, which 

 radiate in all directions like the fingers from the palm of the 

 hand ; hence, such a leaf is said to be palmntely veined. 

 Net-veined leaves — the plantain 

 (Fig. 209), wild smilax, beech, dog- 

 wood — are sometimes ribbed in a 

 way that might lead an inexperi- 

 enced observer to confound them 

 with parallel-veined ones, but the 

 reticulations between the ribs show 

 that they belong to the net-veined 

 class. 



173. Veins as a mechanical sup- 

 port. — Hold up a stiff, firm leaf of any kind, like the mag- 

 nolia, holly, or India rubber, to the light, having first scraped 

 away a little of the under surface, and examine it with a lens. 

 Compare it with one of softer texture, like 

 the peach, maple, or clover. In which are 

 the veins the closer and stronger? Which 

 is the more easily torn and wilted ? Tear a 

 blade of grass longitudinally and then cross- 

 wise ; in which direction does it give way 

 the more readily ? Tear apart gently a leaf 

 of maple, or ivy, and one of elm or other 

 pinnately veined plant; in which direction 

 does each give way with least resistance? 

 What would you judge from these facts as 

 to the mechanical use of the veins ? 



174. Effect upon shape. — By comparing 

 a number of leaves of each kind it will l^e seen that the 

 feather-veined ones tend to assume elongated outlines (Figs. 

 197, 207) ; the palmate-veined ones, broad and rounded forms 

 (Figs. 195, 208). Notice also that the straight, unbroken 

 venation of parallel- veined leaves is generally accompanied by 

 smooth, unbroken margins, while the irregular, open meshes 

 of net-veined leaves are favorable to breaks and indentations. 



Fig. 209. — Ribbed 

 leaf of plantain. 



