104 MODIFIED CIRCUMNUTATION. Chap. VII 



single large ellipse is described during each twenty-foui 

 hours. Such ellipses are generally narrow and ver- 

 tically directed, for the amount of lateral movement is 

 small. That there is some lateral movement is shown 

 by the ascending and descending lines not coinciding, 

 and occasionally, as with Besmodium gyrans and Thalia 

 deallata, it was strongly marked. In the case of Meli- 

 lotus the ellipses described by the terminal leaflet 

 during the day are laterally extended, instead of ver- 

 tically, as is usual ; and this fact evidently stands in 

 relation with the terminal leaflet moving laterally 

 when it goes to sleep. With the majority of sleeping 

 plants the leaves oscillate more than once up and 

 down in the twenty-four hoi?rs ; so that frequently two 

 t;llipses, one of moderate size, and one of very large size 

 which includes the nocturnal movement, are described 

 within the twenty-four hours. For instance, a leaf 

 which stands vertically up during the night will sink 

 in the morning, then rise considerably, again sinlv in 

 the afternoon, and in the evening reascend and assume 

 its vertical nocturnal position. It will thus describe, 

 in the course of the twenty-four hours, two ellipses of 

 unequal sizes. Other plants describe within the same 

 time, three, four, or five ellipses. Occasionally the 

 longer axes of the several ellipses extend in different 

 directions, of which Acacia Farnesiana offered a good 

 instance. The following cases will give an idea of the 

 rate of movement : OoeaUs acetosella completed two 

 ellipses at the rate of 1 h. 25 m. for each ; Marsilea 

 quadrifoliata, at the rate of 2 h.; TrifoUum subferraneum, 

 one in 3 h. 30 m. ; and Arachis liypogsea, in 4 h. 50 m. 

 But the number of ellipses described within a given 

 time depends largely on the state of the plant and 

 on the conditions to which it is exposed. It often hap- 

 pens tliat a single ellipse may be described during one 



