TIIKTR FOmrS. 



1.37 



¥ less abundance of the parenchyma in which (he veins are distrib- 

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



245 147 2)8 



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 ellip- 

 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 mid- 

 dle of the blade, the leaf becomes obovate (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), &c, when the 

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

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



FIG 245-253. Forms of simple, chiefly radiated-veined leaves. 



14 



