10 



PLANT RELATIONS. 



14. Motile leaves, — There are leaves, however, which 

 have no fixed light position, but are so constructed that 

 they can shift their position as the direction of the light 

 changes. Such leaves are not in the same position in the 



afternoon as in the 

 forenoon, and their 

 night position may he 

 very different from 

 either (see Figs. 2, ■iti, 

 ob, 4). Some of the 

 common house ])lants 

 show this jHiwer. In 

 the case of the com- 

 mon Ox/ilix the night 



Fi.. 3.. The day positioa of the leuv.s of redbad POsition of the leaveS 



(6'f (lis).— After Aktuur. is remarkably different 



from the position in light. 

 If such a plant is exposed 

 to the light in a window and 

 the positions of the leaves 

 noted, and then turned 

 half way around, so as to 

 bring the othur side to the 

 light, the leaves may be 

 observed to adjust them- 

 selves gra.dually to the 

 changed light-relations. 



15. Compass plants. — A 

 striking illustration of a 



special light position is found in the so-called "compass 

 plants." The best known of these plants is the rosin-weed 

 of the i^rairie region. Growing in situations exposed to 

 intense light, the leaves are turned edgewise, the flat faces 

 being turiied away from the intense rays of midday, and 

 directed towards the rays of less intensity ; that is, those of 



Pig. 3li. The night position of the leaves 

 of redbud (Cerri.i).— After Aktiiuk. 



