10 



PLANT STUDIES 



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

 have no hxed light position, bnt are so constructed that 

 they can shift their position as the direction of tlie li^^ht 

 clianges. Such leaves are not in the same position in tlie 



afternoon as in I lie 

 forenoon, and tlieir 

 night position may lie 

 very diiferent fi-om 

 either (see l-'igs. ".'. 'Aa. 

 '.lb, 1). Some of the 

 common lujuse jilants 

 show tliis ]iower. In 

 the ease of the com- 

 mon O.ralls the inght 



„ „ „, J .,. , ^^ , . ,, , liosition of tlie loaves 



Fig. 3a. The day position of the leaves of redhnd f 



(C'«ra»).— After Arthur. is romai'kalilv (lilTei'ent 



from the position in liglit. 

 If sucli a plant is exposed 

 to tlie light in a window and 

 the positions of the leaves 

 noted, and then turned 

 half way around, so as to 

 bring the other side to the 

 light, the leaves may he 

 observed to adjust them- 

 selves gradually to the 

 changed light-relations. 



l.T. Compass plants. — A 

 striking illustrati(,in of a 



special light jiosition is found in the so-callcil ■■ conijiass 

 ]ilants." The best known of these jilants is the rosin-wood 

 of the })rairie I'egion. Growing in situations oxposeil lii 

 intense liglit, the leaves are turned edgewise, the llnl faces 

 Ijcing turned away from the intense rays of middav, and 

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



Fig. 3*. The night posilion of the leaves 

 of reaiiud ( rfivvV).— After Aiernri:. 



