10 
PLANT STUDIES 
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 be 
very different from 
either (see Figs. 2, 3#, 
3, 4). Some of the 
common house plants 
show this power. In 
the case of the com- 
mon Oxalis the night 
Fzo. 8a. The day position of the leaves of redbud P 0sition <>f the leaves 
). After ARTHUR. 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 other side to the 
light, the leaves may be 
observed to adjust them- 
selves gradually 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 prairie region. Growing in situations exposed to 
intense light, the leaves are turned edgewise, the flat faces 
being turned away from the intense rays of midday, and 
directed towards the rays of less intensity ; that is, those of 
FIG. 36. The night position of the leaves 
of redbud (Cercis). After ARTHUR. 
