96 



STRUCTURAL BOTANY. 



development and extension of the parenchyma, it follows that 

 there will be the greatest extension of outline where the veins 

 are largest and most numerous. Consequently the form of the 

 leaf will depend upon the direction of the veins and the vigor 

 of their action in developing the intervening tissue. In accord- 

 ance with this theory, leaf-forms will be classed in respect to 

 their venation. 



314 



Forms oflenrfs. 311, Rhododendron maximum. 312, Alnus glntinosa (cult.). 313, Polygonum dtim- 

 etonim. 314, Pawpaw. 315, Impatiens fulva. 316, Celfis Americana. 317, Oircaea Lutetiana. 313, 

 Catmint. 319, Solidago Canadensis a tripli-veined leaf. 



288. Feather- veined leaves. Of these, the following 

 forms depend upon the length of the veinlets in relation to eacli 

 other and to the midvein. When the lower veinlets are longer 

 than the others, the form of the blade will be (1) ovate, with the 

 outline of an egg, the broad end at the base ; (2) lanceolate, or 

 lance-shaped, narrower than ovate, tapering gradually upward; 

 (3) deltoid, or triangular-shaped, like the Greek letter A. 



289. If the middle veinlets exceed the others in length, the leaf 

 will be (4) orbicular, roundish, or quite circular; (5) elliptical, 

 with the outline of an ellipse, nearly twice longer than broad ; 

 (6) oval, broadly elliptical; (7) oblong,. narrowly elliptical. 



290. When the veinlets are more largely developed in the upper 

 region of the leaf, its form becomes (8) obovate, inversely ovate, 

 the narrow end at base; (9) oblanceolate, that is, lanceolate with 



