LEAVES SERVING SPECIAL OFFICES. 113 



221. The pitcher-bearing leaf in Nepenthes has been referred 

 to (218, Fig. 222) : of this there are various species, all of them 

 somewhat wood}' climbing 



plants of tropical Asiatic 

 and African islands of 

 the southern hemisphere, 

 some of them familiar in 

 conservatory cultivation. 

 Here the tendril may be 

 regarded as a prolonged 

 extension of the midrib 

 of the blade, and the 

 pitcher, with its hinged 



lid, as a peculiar development from its apex. The 

 water contained in the pitcher is a secretion, much 

 of which appears before the lid opens ; and a sweetish 

 excretion at the orifice lures insects. The presence 

 of these in the pitcher increases the watery secre- 

 tion in which the animals are drowned ; and this 

 secretion is ascertained to have a certain digestive 

 power. 1 



222. The aquatic sacs of Utricularia or Bladder- 

 wort are diminutive ascidia, always under water, 



and with lid opening inward, like a valve, preventing the exit 

 of minute animals entrapped therein. 2 Morphologically, they 

 are doubtless leaves or parts of leaves. 



223. As Sensitive Fly-traps. The leaves of all species of 

 Drosera or Sundew are beset with stout bristles tipped with a 

 gland, which secretes and when in good condition is covered 

 b}' a drop of a transparent and very glairy liquid, sufficiently 

 tenacious to hold fast a fly or other small insect. Adjacent 

 bristles, -even if not touched, in a short time bend towards those 

 upon which the insect rests, and thus bring their glands also 

 into contact with it. In Drosera filiformis, the leaves are fili- 

 form, with no distinction of petiole and blade. In D. rotundifolia 

 and other common round-leaved species, there is a clear distinc- 



1 This was first made out by J. D. Hooker, and announced in his address, 

 as President of the British Association for the Advancement of Science, at 

 Edinburgh, 1871. 



2 Darwin, Insectivorous Plants, 395. Cohn, Beitrage zur Biologic der 

 Pflanzen, 1875. Mrs. Treat, in The Tribune, New York, September, 1874, 

 and Card. Chron. 1875, 303. 



FIG. 228. Pitcher of Darlingtonia California, 229. Pitcher of Cephalotus follicu- 

 laria, with lid open. 



