380 



LIFE ON THE EARTH 



FIGURE 118 



edge of the leaf is toward the sun, the leaf thus maintaining 

 a nearly vertical position all day, with its greatest length 

 extending in a nearly north and south line. 

 It is the effort to regulate the amount of 

 light falling on the leaf, and not any mag- 

 netic influence, which causes the leaf to 

 point in the direction of the compass needle. 

 The shapes of the leaves vary greatly in 

 different plants. Sometimes they assume 

 very singular forms, as in the pitcher plant 

 (Figure 118) and Jack-in-the-pulpit. Some- 

 times they even become carnivorous, as in 

 the sundew and Venus flytrap. 

 Around the margin of the sun- 

 dew leaf and on the inner sur- 

 face are a number of short 

 bristles, each having at the end 

 a knob which secretes a sticky 

 liquid. As soon as an insect 

 touches one of these knobs, it 

 sticks to the knob and the other 

 bristles begin to close in upon 

 the insect and hold it fast. Soon 

 the insect dies and the leaf se- 

 cretes a juice which digests the 

 soluble parts of the insect. 



In the Venus flytrap (Figure 

 119) the leaf terminates in a 

 portion which is hinged at the 

 middle and has on the inside 

 of each half three short hairs, while the outside is fringed 

 by stiff bristles. As soon as an insect touches the hairs, 



FIGURE 119 



