134 LEAVES AND BUDS. 



usually project as ridges on the under-surface, but the smaller veinlets 

 are buried in the tissue of the leaf. The arrangement of the smaller 

 veinlets and the number of the larger veins differ in different leaves. 

 This is what is termed the venation of the leaf. 



Note that the leaves of all grasses, orchids, flags, wild hyacinths, 

 arid daffodils have all their principal veins running parallel through the 

 entire length, and that these leaves are more or less elongated and 

 blade-like. The leaves of most of our trees and herbs, however, have 

 their principal veins branching off from the midrib on either side, 

 while the smaller ones form a delicate network such as we observed 

 in the bean leaf. The former arrangement (parallel venation) is 

 characteristic of Monocotyledons, the latter (reticulate venation) of 

 Dicotyledons (but also found in some Monocotyledons, e.g. Arum). 



If leaves are allowed to decay in water until the softer parts can be 

 brushed away, skeletons of the harder parts can be obtained which 

 directly exhibit the venation, but in most cases it is sufficient to 

 hold up the leaf to the light to render the smaller veins plainly 

 visible. 



168. Simple and Compound Leaves. Some leaves are simple ; 

 that is, their flat part or blade (lamina) is not divided into distinct 

 portions, though they may be very deeply divided. Such is the case 

 with the leaves of the Oak, Hazel, Ivy, Dandelion, etc. These simple 

 leaves exhibit a great variety of form, and the student should make a 

 series of drawings illustrating the more typical shapes. 



In compound leaves, of which we have already seen an example in 

 the Bean, the blade is divided into distinct parts called leaflets, which 

 may be arranged in opposite pairs along the central stalk as in Rose, or 

 may all radiate from one point of the stalk as in Horse Chestnut. 



The outline of the lamina assumes a great variety of forms, and 

 special technical terms are given to the more strongly marked and 

 more commonly occurring of these. All gradations exist between 

 leaves of widely different shape, and since no general principles are 

 involved in the application of these terms, they need not be discussed 

 here. The following list includes the commonest shapes : 



(1) Blade broadest near the base e.g. cordate (heart-shaped), 

 sagittate (arrow-head-shaped), reniform (kidney-shaped), ovate 

 (egg-shaped), lanceolate (lance-head-shaped, much longer than broad, 

 tapering to pointed tip). 



(2) Blade broadest near the tip e.g. obcordate, obovate, 

 oblanceolate (outline as in cordate, ovate, and lanceolate, but 

 with the narrow end at the base), spathulate (spoon-shaped, e.g. 

 Daisy). 



(3) Blade as broad in the middle as anywhere else e.g. long 

 narrow forms, as acicular (needle-shaped), linear (long and narrow, 

 with parallel margins), cylindrical ; and rounded forms, as orbicular 

 (circular), elliptical, oval, peltate (shield-like, blade nearly circular, 

 but with stalk near the middle of lower surface). 



