CHAP. II. LEAVES. 119^ 
a lid termed the operculum. To me it appears that the pitcher 
itself, or fistular part, is the petiole, and the operculum the 
blade of a leaf in an extraordinary state of transformation. 
Look, for example, at Dionsea muscipula ; in this plant the 
leaf consists of a broad-winged petiole, articulated with a col- 
lapsing blade, the margins of which are pectinate and 
inflexed. Only suppose the broad-winged petiole to collapse 
also, and that its margins, when they meet, as they would in 
consequence of a collapsion, cohere ; a fistular body would 
then be formed,, just like the pitcher of Sarracenia (^^. 58.B), 
and there would be no difficulty in identifying the acknow- 
ledged blade of Dionaea with the operculum of Sarracenia 
also. From Sarracenia the transition to Nepenthes {fig, 58. A) 
would perhaps not be considered improbable. 
59 
The student must not, however, suppose that all pitchers 
are petioles, because those of Nepenthes and Sarracenia are 
so. Those of the curious Dischidia Rafflesiana {fig. 59.), 
figured by Wallich in his PlantcB AsiaticcB Rariores, are 
leaves, the margins of which are united. The pitchers of 
Marcgraavia and Norantea {fig. 60.) are bracts in the same 
state. 
Spines of the leaves are formed either by a lengthen- 
ing of the woody tissue of the veins, or by a contraction 
I 4 
