12. THE LEAF. 



3!) 



parallel to each other, and then turn towards the apex of the leaf (e.g. 

 Canna, Musa, etc.). 



c. The venation is said to be reticulate, when the veins branch repeatedly 

 at various angles, and the branches for the most part anastomose (Fig. 26). 

 Some of them, however, end blindly in the meshes of the network. This 

 kind of venation is characteristic of Dicotyledons" ; but it also occurs in 

 some Monocotyledons (e.g. Paris, Dioscorea, Smilax, many Aracese) and 

 many Ferns. 



The Different Kinds of Leaves. The leaves of different plants, 

 as might be expected, are not alike, but differ more or less widely 

 in size, shape, colour, and texture. But even the leaves borne on 



FIG. 25. Apex of a Grass-leaf showing 

 parallel venation : 711 middle vein ; a ana- 

 stomoses ; D veinlets. (x4.) 



FIG. 26. Portion of a leaf of Salix Ca- 

 prea with reticulate venation : TO midrib ; 

 n the larger lateral ribs ; c the anasto- 

 mising veins (nat. size). 



one and the same plant are not all alike, the reason of their dissimi- 

 larity being that, as there are different functions to be performed, 

 the leaves are variously adapted in form and structure to the per- 

 formance of these functions. 



1. Foliage-leaves are usually known simply as leaves (Fig. 27 

 Li). They are conspicuous on account of their green colour, and in 

 accordance with their nutritive function (see Part III.) they are 

 expanded as much as possible to the sun-light. If they are small 

 they are very numerous (Conifers), and the larger they are the 

 fewer they are (Sunflower, Paulownia). They nearly always 



