DIURNAL MOVEMENTS IN PLANTS 



529 



Epinasty and Hyponasty : Exjjerimen t 203 . — There are 

 other autonomous movements which are relatively slow. 

 Kven in an erect stem there may be a to and fro oscillation. 

 In such a case the effect of an external stimulus, say of 

 light, is one of algebraical summation. The following is 

 the summary of results of unilateral action of light on 

 the nutating hypocotyl of a pea seedling : 



Figure 189 exhibits the effect of light applied alternately 

 above or below the cotyledon of Oucurbita Pepo. On 



Fig. 189. — Effect of unilateral light on hyponaslic movement of tiip cotyledon 

 of Pepo. Application of light indicated by arrows; light acting from below 

 retards, acting from above accelerates the movement. The last part of the 

 C'lrve in each .shows recovery on the stoppage of light. 



account of the more rapid growth of the lower side, the 

 cotyledon was exhibiting a hyponastic up-movement. 

 .Application of light from above enhanced the existing rate 



