THEIR FORMS. 



157 



less abundance of the parenchyma in which the veins are distrib- 

 uted. This view is readily inteUigible upon the supposition that a 



leaf is an expansion of soft parenchyma, in which the firmer veins 

 are variously ramified. Thus, if the principal veins of a feather- 

 veined leaf are not greatly prolonged, and are somewhat equal in 

 length, the blade will have a more or less elongated form. If the 

 veins are very short in proportion to the midrib, and equal in length, 

 the leaf will be linear (as in Fig. 240) ; if longer in proportion, 

 but still equal, the leaf will assume an oblong form (Fig. 242), 

 which a slight rounding of the sides converts into an oval or eUi'p- 

 tical outline. If the veins next the base are longest, and especially 

 if they curve forward towards their extremities, the leaf assumes a 

 lanceolate (Fig. 239), ovate (Fig. 241), or some intermediate form. 

 On the other hand, if the veins are more developed beyond the midr 

 die of the blade, the leaf becomes ohovate (Fig. 232), or cuneiform 

 (Fig. 235). In radiated or palmately veined leaves (Fig. 245-253), 

 where the primary ribs are divergent, an orbicular or roundish out- 

 line is most common. When some of the ribs or their ramifications 

 are directed backwards, a recess, or sinus, as it is termed, is pro- 

 duced at the base of the leaf, which, taken in connection with the 

 general form, gives rise to such terms as cordate or heart-shaped 

 (Fig. 244), reniform or kidney-shaped (Fig. 245), t&c, when the 

 posterior portions are rounded ; and those of sagittate or arrow- 

 headed (Fig. 252), and hastate or hdWerd-shaped (Fig. 250), when 



no. 246 - 253. Forms of Bimple, chiefly radiated-Teined leaves. 



14 



