1G6 



THE XEAVES, 



■ upper surface of a folded leaf cohere, those of some other plants ex- 

 hibit a cohesion by their contiguous edges, and give rise to a differ- 

 ent anomaly. This is illustrated by peltate 

 leaves (Fig. 248), and more strikingly by 

 what are termed perfoliate leaves. These in 

 some cases originate from the union of the 

 bases of a pair of opposite sessile leaves {con- 

 nate-perfoliate), as in Silphium perfoliatum, 

 Triosteum perfo- 

 liatum, and the 

 upper pairs of 

 true Honej^suckle 

 (Fig. 294). In 

 others they con- 

 sist of a single 

 clasping leaf, the 

 posterior lobes of 

 which encompass the stem and cohere 

 on the opposite side, as is seen in Bu- 

 pleurum rotundifolium, Uvularia perfo- 

 liata, and Baptisia perfoliata (Fig. 293). 



296. leaves with no distinction of Blade 



and Petiole. The leaves of the Iris, as 

 weU as those of the Daffodil, the Onion, 

 and of many other Endogens, show no 

 distinction of blade and petiole. In some the leaf of this sort may 

 be regarded as a sessile blade ; in others, rather as a petiole per- 

 forming the functions of a blade. Leaves are not always expanded 

 bodies. Sometimes they are filiform or thread-shaped, as those of 

 Asparagus : some are acicular, acerose, or needle-shaped, as in Pines 

 and Larches (Fig. 212, 213) ; others are subulate or awl-shaped, as 

 in Juniper, &c. The Red Cedar and Arbor Vitse (Fig. 295) exhibit 

 both awl-shaped and scale-shaped leaves on different branchlets. 



297. Succulent or Fleshy Leaves, like those of Stonecrop, House- 

 leek, Mesembryanthemum or Ice-Plant, and the Agave or Century- 

 Plant, usually assume shapes more or less unlike ordinary foliage. 

 Some of them are terete, hke stems, or at least have no distinct 

 upper and lower surface. These greatly thickened leaves serve a 



FIG. 293. Perfoliate (single) leaves of Saptisia perfoliata. 



FIG. 294. Connate-perfoliate leaves of a wild Honeysuckle (Lonicera iiava). 



