124 



Introduction to Botany. 



Such movements are in harmony with the functions of 

 the leaf, for the leaflets are spread out to receive the 

 light necessary to photosynthesis in the daytime, and are 

 folded together in the nighttime so that they are less apt 

 to receive injury from too great radiation of heat or from 

 the beating of storms. The variations in the turgidity of 

 the motor organs are induced and regulated by the proto- 

 plasts, which are influenced in their action by variations in 



Fig. 6o. 



Motor organs (a, i, and c) of Scarlet Runner in their day position at .4, and in their 

 night position at B. C, a cross section of a petiole, and Z) of a motor organ. 

 After Sachs. 



light intensity. Periodic movements induced by alterna- 

 tions of day and night may be observed in the oxalises 

 (commonly represented by the violet and yellow wood 

 sorrel) and in many members of the pulse family. 



97. The Sensitive Plant. — Movements of the leaves of 

 some plants may be induced by contact with a solid body, 

 by shaking the entire plant, by intense illumination, or by 

 chemical stimulus, etc. The sensitive plant, ]\Iiinosa pudica^ 



