THEIR FORMS. 



159 



danlly developed, as in fact happens in the upper leaves of the same 

 species when they grow out of water, and is shown in the same 

 figure, they are merely cleft or lobed. If these lobes grow together 

 nearly to the ex- 

 tremity of the /vl /X \ FT' 

 principal veins, rJ ^pia-V 

 the leaf is only [ V ^J 

 toothed, serrated, J y 

 or crenated; and 

 if the small re- 

 maining notches 

 were filled with 

 parenchyma, the 

 leaf would be en- 

 tire. The study 



of the development of leaves, however, proves that the parenchyma 

 grows and shapes the outlines of the organ in its own way, irrespec- 

 tive of the framework, which is, in fact, adapted to the parenchyma 

 rather than the parenchyma to it. The principal terms which designate 

 the mode and degree of division in simple leaves may now be briefly 

 explained, without further reference to this or any other theory. 



282. A leaf is said to be serrate, when the margin is beset with 

 sharp teeth which point forwards towards the apex (Fig. 254) ; 

 dentate, or toothed, when the sharp salient teeth are not directed 

 towards the apex of the leaf (Fig. 255); and crenate, when the 

 teeth are rounded (Fig. 248, 256). A slightly waved or sinuous 

 margin is said to be repand (Fig. 257) ; a more strongly uneven 

 margin, with alternate rounded concavities and convexities, is termed 

 sinuate (Fig. 258). When the leaf is irregularly and sharply cut 

 deep into the blade, it is said to be incised (Fig. 259) ; when the 

 portions (or segments) are more definite, it is said to be lobed (Fig. 

 260, 264) ; and the terms two-lobed, three-lobed (Fig. 264), fve-lobed, 

 &c, express the number of the segments. If the incisions extend about 

 to the middle of the blade, or somewhat deeper, and especially if the 

 sinuses are acute, the leaf is said to be cleft (Fig. 261, 265) ; and 

 the terms two-cleft, three-cleft (Fig. 265), &c. (or in the Latin form, 

 bifid, trifid, &c), designate the number of the segments : or when 

 the latter are numerous or indefinite, the leaf is termed many-cleft, 

 or multifid. If the segments extend nearly, but not quite, to the 



FIG 254 - 259 Forms of leaves as to the toothing of their margins. 



