THE MOVEMENTS OF PLANTS. 



183 



plants. The motor organ in the Venus' fly-trap (figs. 224, 

 137) is the cushion of tissue running along the back of the 

 leaf between the two lobes. By the sudden variation in 

 turgor of some of these cells the two halves of the leaf are 

 thrown quickly together when one of the six bristles upon its 



Fig. 138. Fig. 139. 



Fig. 137. — Part of a transverse section of a leaf of Venus' fly-trap, m, the cushion of 

 tissue constituting the motor organ ; b, one of the sensitive bristles which, upon being 

 touched, cause the leaf to close : ^, one of the interlocking teeth. _The_minute pro- 

 jections over inner (ventral) surface are glands which secrete the digestive fluid and 

 later absorb the food. Magnified about 5 diam.— After Kurz. 



Fig. 138. — A leaf of the sensitive plant fully expanded. Natural size. — After Duchartre. 



Fig. i3g. — A leaf of the sensitive plant after stimulation The motor organ at the base 

 of each leaflet lias thrown it forward and upward ; the motor organs at the base of 

 the four divisions have moved them together. The motor organ at the base of the 

 main petiole has moved the whole leaf sharply downward. Natural size.-After 

 Duchartre. 



upper surface is touched. The sensitive plant drops one of 

 its leaflets or the whole leaf quickly when stimulated by con- 

 tact, heat, or electricity. The position of the leaves when 

 normally expanded is shown in figure 138, and their position 

 after stimulation by figure 139. The stamens (1 287) of 

 some flowers and the stigmas {^ 283) of others are sensitive 



