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. 



315 fv-r- 



317 



314 



Forms of leaves. 311, Rhododendron maximum. 312, Alnus glutinosa (cult.X 313, Polvgonum dint 

 ' , 316, Celt 

 reiued leaf. 



ctorum. 314, Pawpaw.' 315, Impatiens fulva. 316, Celtis Americana. 317, Oimea Lutetiana. 

 Catmint. 319, Solidago Canadensis a tripli-ve " 



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

 forms depend upon tho length of the veinlets in relation to each 

 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 



