388 MODIFIED CIRCUMNUTATION. CHAP. VII. 



Euphorbia jacguitiiceflora (Euphorbiacese). Mr. Lynch 

 called our attention to the fact that the young leaves of this 

 plant sleep by depending vertically. The third leaf from the 

 summit (March IJth) was inclined during the day 30 beneath 

 the horizon, and at night hung vertically down, as did some of 

 the still younger leaves. It rose up to its former level on the 

 following morning. The fourth and fifth leaves from the summit 

 stood horizontally during the day, and sank down at night only 

 38. The sixth leaf did not sensibly alter its position. The 

 sinking movement is due to the downward curvature of the 

 petiole, no part of which exhibits any structure like that of 

 a pulvinus. Early on the morning of June 7th a filament was 

 fixed longitudinally to a young leaf (the third from the summit, 

 and 2f inches in length), and its movements were traced on 

 a vertical glass during 72 h., the plant being illuminated from 

 above through a skylight. Each day the leaf fell in a nearly 

 straight line from 7 A.M. to 5 P.M., after which hour it was so 

 much inclined downwards that the movement could no longer 

 be traced ; and during the latter part of each night, or early in 

 the morning, the leaf rose. It therefore circumnutated in a 

 very simple manner, making a single large ellipse every 24 h., 

 for the ascending and descending lines did not coincide. On 

 each successive morning it stood at a less height than on the 

 previous one, and this was probably due, partly to the increasing 

 age of the leaf, and partly to the illumination being insufficient ; 

 for although the leaves are very slightly heliotropic, yet, accord- 

 ing to Mr. Lynch's and our own observations, their inclination 

 during the day is determined by the intensity of the light. On 

 the third day, by which time the extent of the descending 

 movement had much decreased, the line traced was plainly 

 much more zigzag than on any previous day, and it appeared 

 as if some of its powers of movement were thus expended. At 

 10 P.M. on June 7th, when the leaf depended vertically, its move- 

 ments were observed by a mark being placed behind it, and the 

 end of the attached filament was seen to oscillate slowly and 

 slightly from side to side, as well as upwards and downwards. 



Phyllanthus Niruri (Euphorbiacese). The leaflets of this 

 plant sleep, as described by Pfeffer,* in a remarkable manner, 

 apparently like those of Cassia, for they sink downwards at 

 night and twist round, so that their lower surfaces are turned 



* Die Period. Beweg.,' p. 159. 



