330 



MODIFIED CIECUMNUTATION. 



Chap. Vn 



Averrhoa hilimhi (Oxalidae).— It has long been known,* firstly 

 that the leaflets in this genus sleep ; secondly, that they move 

 spontaneously during the day ; and thirdly, that they are sensi- 

 tive to a touch; but in none cf these respects do they diffei 

 essentially from the species of Oxalis. They differ, however, as 

 Mr. E. I. Lynch f has lately shown, in thoir spontaneous move- 

 ments being strongly marked. In the case of A. bilimbi, it is a 

 wonderful spectacle to behold on a warm sunny day the leaflets 

 one after the other sinking rapidly downwards, and again 

 ascending slowly. Their movements rival those of Desmodium 

 qyrans. At night the leaflets hang vertically down ; and now 



Fig. 132. 



Arerrhoi bilimbi : leaf asleep ; drawing reduced. 



they are motionless, but this may be due to the opposite ones 

 being pressed together (Fig. 132). The main petiole is in con- 

 stant movement during the day, but no careful observations were 

 made on it. The following diagrams are graphic representa- 

 tions of the variations in the angle, which a given leaflet makes 

 with the vertical. The observations were made as follows. 

 The plant growing in a pot was kept in a high temperature, 

 the petiole of the leaf to be observed pointing straight at 

 the observer, being separated from him by a vertical pane of 

 glass. The petiole was secured so that the basal joint, or pul- 

 vinus, of one of the lateral leaflets was at the centre of a gradu- 

 ated arc placed close behind the leaflet. A fine glass filament 

 was fixed to the leaf, so as to project like a continuation of the 



♦ Dr. Bruce, 'Philosophical Trans.,' 1785, p. 356. 

 'Journal Linn. Soo.,' vol. xvi. 1877, p. 231. 



