174 THE LEAVES. 



eral plants of widely different families. If we conceive the mar- 

 gins of the dilated petiole of Dionaea to curve inwards until they 

 meet, and cohere with each other, there would result a leaf not 

 unlike that of Sarracenia purpurea, the common Pitcher-plant or 

 Sidesaddle Flower of the Northern United States (Fig. 224), in 

 which, accordingly, the tube or pitcher may be considered as the 

 petiole, and the hood at the summit as the lamina. This view is 

 confirmed by a new Pitcher-plant of the same family ( Heliampho- 

 ra, Fig. 223), recently discovered by Mr. Schomburgk in the 

 mountains of British Guiana, and described by Mr. Bentham ; in 

 which the margins of the dilated petiole are not always united 

 quite to the summit, and the lamina is represented by a small 

 concave terminal appendage. In the curious Nepenthes (Fig. 

 225), the petiole is first dilated into a kind of lamina, then con- 

 tracted into a tendril, and finally dilated into a pitcher, contain- 

 ing fluid secreted by the plant itself; the orifice being accurately 

 closed by a lid, which is from analogy supposed to represent the 

 real blade of the leaf. 



303. The cohesion of the edges of a leaf with each other, or 

 with neighbouring organs, is by no means infrequent ; -since all 



parts or organs of a plant which are contigu- 

 ous at the time of their development are liable 

 to become ingrafted or to cohere together. 

 This is illustrated by the formation of peltate 

 leaves (Fig. 203, 204), and likewise by what 

 are termed perfoliate leaves ; whether formed 

 by the union of the bases of a pair of opposite 

 sessile leaves (connate-perfoliate), as in Sil- 

 phium perfoliatum, Triosteum perfoliatum, 

 the upper pairs of the Honeysuckle, &c. ; or 

 consisting of a single clasping leaf, the pos- 

 terior lobes of which encompass the stem and 

 cohere on the opposite side, as is seen in 

 Bupleurum rotundifolium, Uvularia perfoliata, 

 and Baptisia perfoliata (Fig. 229). 



304. Stipules (259) are lateral appendages of leaves, usually in 

 the form of small foliaceous bodies, situated on each side of the 

 base of the petiole (Fig. 215, &c.). They are not found at all in a 



FIG. 229. Perfoliate leaves of Baptish perfoliata. 



