176 



THE LEAF 



may be either biennial, the onHnary form, or perenniah Persistent 

 leaves are those which remain upon the tree, but in a dead condition, 

 being usually forced off by the growth of the following season. 



The Lamina. — Coming now to the consideration of the leaf-blade, we 

 note that it is to be studied, and its varieties classified, with regard to 

 its relation to its support, its texture, surface, form — this including the 

 general outline as well as special forms of apex and base — venation, 

 margin, division, and modification of form and function. 



Relation of the Leaf-base to the Plant-stem. — When a i)etiole or a 

 lamina has grown fast for a portion of its length to the plant stem, it is 

 called Adnate (Fig. 477). One whose base is heart-shaped and surrounds 

 the plant stem, whether growing fast to it or not, is called Amplexicaul 



47Z 



Modifications of the leaf-base: Fig. 476. Connate-perfoliate (boneset). 477. Adnate to plant stem 

 {V erhascum) . 478. Sessile (Solidago). 479. Amplexicaul (^Asler Novae-Angliae). 480. Perfoliate 

 {Oakesia). 481. Margined {PlaiUago). 482. Continuous. 483. Intramarginal-peltate. 



or Clasping (Fig. 479). When the basal lobes of a clasping leaf entirely 

 surround the stem and become connate upon the other side, so that the 

 Stem appears to be growing up through a perforation in the leaf, the 

 leaf is called Perfoliate (Fig. 480). When opposite leaves are connate 

 by their bases they are called Connate or Connate-perfoliate (Fig, 476). 

 When the bases of sheathing leaves clasp the stem in such a manner as 

 to present a V-shape in transverse section, and one is superposed upon 

 another in the same manner, they are called Equitant. 



Relation of the Base to the Petiole. — As to the attachment of the blade 

 to the petiole, the leaf is Peltate when this insertion is intra-marginal 

 through the connation of the edges of basal lobes. A peltate leaf may 

 be Centrally (Fig. 473), or Eccentrically (Fig. 483) peltate. When the 

 petiole changes so gradually into the lamina that it is impossible to 



