240 



BOTANY OF THE LIVING PLANT 



pl.Hi.lul.il- cells. This has been studied very thoroughly in the Sundew 

 :, in which the mechanism of capture has already been 

 described (p. 164). The secretion which plays so important a part 

 is produced by the glandular head of the tentacle, which receives its 

 vascular supply through a strand traversing its stalk (Fig. 166}. The 

 digestive fluid is exuded by the epithelium that covers the surface 

 of the gland. On contact with an insect, or with a small piece of 



nitrogenous matter, such as a cube of 

 white-of-egg, the gland is stimulated to 

 greater secretion. A proteolytic enzyme, 

 which breaks down the complex protein to 

 simpler soluble substances, is given out, and 

 the secretion takes an acid reaction. The 

 emission of the enzyme and of the acid is, as 

 in the gastric secretion of the animal stomach, 

 dependent upon the absorption of nitro- 

 genous matter from the stimulating body : 

 a piece of indigestible matter produces less 

 secretion and without proteolytic powers. 

 The body of the insect, or the cube of white- 

 of-egg, enveloped in the secretion, is slowly 

 digested, and the dissolved material, together 

 with the secretion itself, absorbed into the 

 cells of the leaf. In the white-of-egg the 

 rounding of the edges of the cube can easily 

 be followed. All that remains of an insect 

 when digestion is complete are the insoluble 

 .>. L 7!?' l6y ' chitinous parts. The process of digestion in 



Pitcher of Nepenthes, with part ° 



of the wall removed to show the the Butterwort and Venus' Flv Trap is 



fluid (F) secreted by the glands . 



bome on the inner surface, essentially the same as in Sundew. The dif- 



(i natural size.) (After Stras- 



burger.) ference lies in the varying perfection of the 



mechanism. 

 In Nepenthes the pitcher-shaped leaves are effective traps for 

 luring small animals into the fluid that partly fills each pendent urn 

 (Fig. 167). In Botanic Gardens these are often choked by the partially 

 digested remains of ants, cockroaches, and other victims. There is 

 no motile mechanism that catches them, but only a static trap. The 

 pitcher's lip slopes inwards, and is cartilaginous and smooth, with 

 secreting glands at its inner rim. Insects attracted by the secretion 

 into a dangerous position on the smooth sloping surface lose their 

 footing and fall into the pitcher, from which, owing to the absence of 



