THE LEAF IN RELATION TO ITS ENVIRONMENT 279 



which have been 

 grouped together for 

 preliminary mention are 

 intimately connected 

 with the phenomena of 

 Variation. 



Of the multifarious 

 leaf forms which the 

 Vegetable World pre- 

 sents, few, perhaps, are 

 so singular as those of 

 the Sarracenias and 

 Nepenthes. These have 

 already been treated at 

 considerable length in 

 Chapter IV., when the 

 insectivorous habits of 

 plants were before us ; 

 and we may therefore 

 dismiss them here in 

 few words. In both 

 genera the insect-catch- 

 ing pitchers are them- 

 selves the leaves, but 

 they have this differ- 

 ence : in Sarracenia the 

 tall trumpet-shaped por- 

 tion of the leaf is looked 

 upon as an expansion 

 of the petiole or leaf- 

 stalk, and the lid as the lamina or blade ; while in Nepenthes the pitcher is 

 regarded as a modification of the lamina, the lid being a special pro- 

 longation of the apex. In the Australian Pitcher-plant (Cephalotus folli- 

 cularis) the parts of the singular tankard-shaped leaves correspond rather 

 with those of Sarracenia than of Nepenthes. Leaves of the pitcher class 

 are called ascidiform, from the Greek askidion, a little bottle. 



Recently, at Kew, one of the attendants pointed out to us a species of 

 Laportea, lately arrived from New Guinea, each of the leaves of which was 

 finished off at the apex as a little cup (fig. 340) ; but we were unable to 

 ascertain what purpose these ascidiform appendages fulfill in the economy 

 of the plant. They can hardly be insect-traps like the pitchers of Nepenthes, 

 as the downward curve of the leaf gives the cups an inverted position. 

 One would like to know whether, in their natural habitat, a vertical position 

 is ever assumed by the leaf. 



Photo by] 



FIG. 341. LIME (Tilia platyphyllos), 



Showing the heart-shaped 



[E. Step. 



and globose fruits with the long bracts 

 attached. 



