ORGANS OF NUTRITION. 



177 



leaves as the Orange {fig. 294), and Venus's Fly-trap {fig. 349). 

 in which the petiole is articulated to the blade ; thus, if we 



Fig. 364. 



Fig. 365. 



Fig. 366. 



Fig. 364. Pitcher of a species of Pitcher plant {Nepenthes distillatoria). p. 



Pitcher closed by the Ud, I. Fig. 365. Pitcher f)f the Side-saddle plant 



{Sarracenia Tpurpurea). Fig. 366. Pitchers of Heliamphora. 



suppose the winged petiole of such plants to fold inwards and 

 unite by its margins, a pitcher would be formed resembling that 

 of Nepenthes, and the jointed blade would then be seen to be 

 clearly analogous to the operculum or lid of that plant. Ac- 

 cording to G-riffith, the pitcher of Nepenthes is a modification 

 of the excurrent midrib or the stalk of the pitcher, and Dr. 

 Hooker has confirmed his observations, and shown that it is 

 formed out of a gland situated at the apex of the midrib. In 

 the Bischidia, the pitchers are considered to be formed by the 

 folding inwards and union of the margins of the blades. 



8. GENERAL VIEW OF THE LEAVES IN THE THREE GREAT 

 CLASSES OF PLANTS, 



We have already seen in describing the structure and general 

 characters of stems and roots, that these present well-marked 

 distinctive characters in the three great classes of plants. The 

 leaves of these three classes also present certain differences, 

 which may be summed up as follows : — 



1. Leaves of Dicotyledonous Plants. — In these the vena- 

 tion is reticulated in consequence of the veins branching in 



N 



