Ill] TYPES OF VENATION 35 



but do Dot directly join, nor do they reach either margin 

 or apex ; this arcuate venation is also characteristic of 

 MelastomacecB, where, however, they curve into the mid- 

 rib above. 



In the case of pronounced pinnate venation, characters 

 of systematic value can also be obtained according as the 

 secondary veins run straight to the margin and there end 

 in the tip of a lobe or tooth, or in the sinus between two 

 lobes or teeth. For instance, they end in the lobes or 

 teeth in Oak, Alder, Hazel, Elm, Chestnut, and other trees 

 and shrubs ; but in Rhinanthacese they end between. 



The palmate or radiate type of venation offers similar 

 variations. Thus the leaves of Cercis are palmate-reticu- 

 late ; those of some Water Lilies are palmate-looped ; 

 those of our ordinary trees and shrubs with palmate vena- 

 tion, where the principal veins radiate but are themselves 

 pinnate, may be termed palmate-pinnate. 



Among parallel-veined leaves we also find several sub- 

 types. In the first place a distinction must be drawn 

 between pseudo-parallel venation as met with in Plantago, 

 Bnpleurum and other leaves, where the venation as a whole 

 is evidently really reticulate, because the smaller veins 

 form visible cross-ties which net together the larger ones ; 

 and also between the curved-parallel venation of Lily of 

 the Valley, Polygonatum, Listera, Potamogeton, &c., as 

 contrasted with the straight-parallel venation observed in 

 Grasses, Sedges, &c. Though even here there are a few 

 invisible cross-ties. 



The fan-like venation of many palms also affords a 

 good character; as also does the furcate venation of many 

 Ferns, Ginkgo, &c. 



Other points to notice regarding venation are whether 

 it is prominent as in the Sallow, or immersed as in thick 

 fleshy leaves like Sedum, and leathery leaves such as those 



32 



