386 



PRACTICAL BOTANY 



FIG. 312. Blade of leaf 

 of sundew without prey 



Somewhat magnified 



(Fig. 312) are borne a number of short bristles, each termi- 

 nating in a knob which is covered with a clear, sticky liquid. 

 When a small insect touches one of the 

 sticky knobs it may be held fast, and in 

 that case the hairs at once begin to close 

 over it, as shown in Fig. 313. The insect 

 soon dies and then usually remains for 

 many days, while the leaf pours out a 

 juice by which the soluble parts of the in- 

 sect are digested. The liquid containing 

 the digested portions is absorbed by the 

 leaf, and contributes an important part 

 of the nourishment of the plant, while 

 the undigested fragments, such as legs 

 and wing cases, remain on the surface 

 of the leaf or may drop off after the hairs 

 let go their hold on the captive insect. 

 356. Pitcher plants. In the ordinary pitcher plants (Fig. 314) 

 the leaf appears in the shape of a more or less hooded pitcher. 

 These pitchers are usu- 

 ally partly filled with 

 water, and in this water 

 many drowned and de- 

 caying insects are com- 

 monly to be found. The 

 insects have flown or 

 crawled into the pitcher, 

 and, once inside, have 

 been unable to escape 

 on account of the dense 

 growth of bristly hairs 

 about the mouth, all 

 pointing inward and 

 downward. The com- 



FIG. 313. Leaves of sundew during diges- 

 tion of captured prey 



The one at the left has all its tentacles closed ; 



the one at the right has half of them closed 



over captured prey. Somewhat magnified 



mon American pitcher plants may not depend much on ani- 

 mal food, but it is certain that some tropical species require it. 



