THE MOVEMENT OF LEAVES 291 
sun.” Others, like the compass plant, turn their edges to 
direct sunlight which is too strong for them. The clover and 
oxalis, which fold their leaflets at night, illustrate the so- 
called “ sleep movements” of plants. The movements of 
sensitive plants are due to the effect of the shock caused by 
Figure 269. — Leaves of Young Plants of Pokeweed. 
Note their large size, and their arrangement to prevent shutting off the 
light from those below. Contrast these leaves with those of Indian Pipe. 
This plant has mere scales in the place of large leaves, and they lack 
chlorophyll, the plant being pure white. It cannot manufacture food for 
itself, but depends on decaying organic matter in the soil. 
touching them. This causes the cells of an organ at the base 
of The petiole, called the pulvinus, to become soft and flaccid 
through loss of water which passes into the inter-cellular 
spaces, allowing the whole leaf to droop and the leaflet to fold. 
HOME WORK, MOVEMENTS OF PLANTS 
Place young seedlings in a window for a day. Which way do they 
turn? Turn the plants around and note how long it takes them to 
become erect; to become bent towards the window again. 
