FORMS OF SIMPLE LEAVES. 



{pelta, a buckler), as in the Castor-oil plant (fig. 161). The edges or 

 margins of orbicular and peltate leaves are often variously divided. 



It has been thought by 

 some that the order of the 

 venation in the leaf bears 

 a close analogy to the ar- 

 rangement of the branches 

 on the stem ; that a cer- 

 tain unity so pervades 

 vegetable organisation, 

 that the root, the stem, 

 and the leaves, may, in 

 their ultimate arrange- 

 ment, be regarded as being 

 typical the one of the 

 Fig. 161. other. M'Oosh states, that 



the angles at which the veins are given off in the leaves are the same 

 as those at which the branches come off from the stem. The angles 

 as given by him vary from 30° to 70°.* 



Without attempting to notice all the forms of leaves, the following 

 are enumerated as the most important. When the veins do not spread 

 out, but run from the base to the apex with a narrow strip of paren- 

 chyma, the leaf is linear or acicular (acus, a 

 needle), (fig. 162), as in Pines and Firs. 

 These trees are hence called in Germany madeZ- 

 hoker, or needle trees. When' the veins 

 diverge, those in the middle being longest, and 

 the leaf tapering, at each end (fig. 181), it be- 



ng. 160. 



162. 



169. 



Pig. 160. Orbicular leaf of Hydroootyle vulgaris. Radiating venation, j), Petiole. ;, 

 Lamina. Fig. 161. Peltate leaf of the Castor-oil plant {RidMus communis). Radiating 

 venation, p, Petiole or leaf-stallt. I, Lamina or blade. Fig. 162. Linear, or acicular leaf 

 of Fir. Pig. 163. Spatlmlate leaf of Daisy. Fig. 164. Oval leaf. Fig. 165. Oblong 

 leaf. Fig. 166. Petiolated, reticulated, somewhat oblong leaf, truncate at the base. 

 Fig. 167. Ovate pointed leaf. Fig. 168. Cordate pointed leaf. Fig. 169. Ovato-lance- 

 olate leaf, i.e. lanceolate in its general contour, but ovate at the base ; doubly serrated, or 

 having large and small serratures alternately at the margin. 



* M'Cosh on the plant morphologically considered. Proceed, of the Bdin. Bot. Soc, 

 July 1851. Bot. Gazette, September 1861. 



