LEAF EXPOSURE TO SUN AND AIR. 101 



plants that they tend to seek the light. The whole plant 

 usually bends toward the quarter from which the strongest 

 light comesy and the petioles bend with it. Such movements 

 may produce very perceptible changes in the course of a few 

 hours. If the position of the plant is shifted after the 

 mature portions have taken a permanent bend, the youngest 



Fig. 87. — Shoots of Dwarf Tropaeolum, showing bending of young shoots 

 toward sunlight. 

 The older portions of the shoots have hent to the left, away from the light (as 

 climbing plants usually do), and toward a close fence. The younger tips of the 

 shoots have bent to the right, the direction from which most light was received. 



portions may be made to bend in the opposite direction, as 

 shown in Tig. 87, and a third bending may then be produced, 

 giving the longer shoots the form of the capital letter S. 



It is not easy to explain in detail how the tissues of the 

 plant act in producing these movements. 



