NVCTITROPIC MOVEMENTS 



68 I 



positive after-effect, the leaf continued to fall till 6 P.M., and 

 that after this it erected itself by a series of five pulsations, 

 until its highest position was attained at about 7 a.m. It 

 next began to exhibit the impressed effect of day, and the 

 leaf then fell rapidly. 



Diurnal response of primary petiole of Mimosa. -In 

 Mii/wsa we merely find the repetition of those movements 

 whose evolution we have already traced through the plagio- 

 tropic stem and the dorsi-ventral petiole. This is made very 



Fig. 274. Continuous, Records of the Diurnal Movement during Thirty- 

 six Hours in Two Specimens of Mimosa 



The continuous line represents the movement of the one-year old, and the 

 dotted line that of the six-months old specimen. The maximum 

 depression is seen to take place at six in the evening, and the recovery 

 nearly completed by midnight. Tliis maximum erection is slightly 

 augmented at dawn. 



apparent in the continuous records which I took of the 

 diurnal movement in two specimens of Mimosa, the records 

 being continued during a period of thirty-six hours (fig. 274). 

 The two plants were placed in an open verandah, and 

 long light indices made, as already described, of peacock's 

 quills, were so attached to the petiole as to form jjrolonga- 

 tions. Records were taken on a vertical revolving drum. 

 A vertical thread was suspended in front of the drum, and 

 the point at which the moving index cut this vertical line 

 was marked at every fifteen minutes. Thus the record gives 



