i6 



FOLIAGE-LEAVES 



(iii.), BLADE or LAMINA. 



The blades of foliage-leaves exhibit great diversities of form 

 and size. 



In form the lamina is usually a flat expanded plate or 

 ribbon-like structure ; but it exhibits all variations from the 

 narrow needle of the Scotch Pine to the circular disk of 

 TropcRolum. Its apex may be drawn out into a fine point 

 or end bluntly, or even terminate in an indentation. The 



margin is even (entire) or 

 uneven (toothed, saw-like, 

 scalloped, etc.). 



Venation of the Lamina. — 

 The substance of the blade is 

 traversed by veins or nerves 

 which frequently stand out 

 more or less prominently. 

 The arrangement of the veins 

 may be grouped under two 

 general headings — (i.) paral- 

 lel-veining ; (ii.) net-like vein- 

 ing. In parallel-veiaed leaves 

 a number of veins, approxi- 

 mately equal in size, run side 

 by side from the base of the 

 lamina towards its tip. The 

 veins are more or less parallel, 

 and are connected by a limited 

 number of smaller ones which 

 join them at right angles. 

 This type of venation is characteristic of Grasses, Lilies, and 

 most other Monocotyledons. In net-veined leaves the finer 

 veins are numerous, and form a complicated network (fig. i8). 

 Most Dicotyledons have net -veined leaves. There are two 

 sub-types of net-like venation — pinnate and palmate veining. 

 A lamina which is pinnately-veined (feather-veined) has a single 

 main vein — the mid-rib — which traverses the centre of the 

 blade, running from the base towards the apex ; this mid-rib 

 gives off from its two sides smaller veins, which are arranged 

 much like the pinnse of a feather — e.g. Hazel (fig. i8). Pear, 

 Primrose. A palmately-veined leaf, in place of possessing a 



Fig. i8. — Venation of Hazel leaf. 

 (After Dennert.) 



