330 



MODIFIED CIECUMNUTATION. 



Chap. VII 



A verrhoa hiliiribi (Oxalidae). — It has long been known,* firstly, 

 that the leaflets in this genus sleep ; seaondly, 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 dififei 

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

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

 ments being strongly marked. In the case of A. hUimhi, 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 

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



Ar^rrhoT. hUimhi : 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. Bruop, 'Philosnpliical Trans.,' 1785, p. 356. 

 ' Jouniul Llun. Sue.,' vol. xvi. 1877, p. 231. 



