376 MODIFIED CIECUMNUTATION. Chap. VII 



was observed every two or three minutes, the plants being kept 

 at a rather high temperature, viz., on the first occasion at 

 77°— 81° F., and the filament then described 2i ellipses in 69 m. 

 On the second occasion, when the temperature was 81° — 86° F., 

 it made rather more than 3 ellipses in 67 m. Therefore, 

 Fig. 157, though now suflSciently complex, would have been in- 

 comparably more so, if dots had been made on the glass every 

 2 or 3 minutes, instead of every hour or half-hour. Althougli 

 the main petiole is continually and rapidly describing small 

 ellipses during the day, yet after the great nocturnal rising 

 movement has commenced, if dots are made every 2 or 3 

 minutes, as was done for aa hour between 9.30 and 10.30 p m. 

 (temp. 84° F.), and the dots are then joined, an almost abso- 

 lutely straight line is the result. 



To show that the movement of the petiole is in all proba- 

 bility due to the varying turgescence of the pulvinus, and not 

 to growth (in accordance with the conclusions of Pfeflfer), a very 

 old leaf, with some of its leaflets yellowish and hardly at all 

 sensitive, was selected for observation, and the plant was kept 

 at the highly favourable temp, of 80° F. The petiole fell from 

 8 A.M. till 10.15 A.M., it then rose a little in a somewhat zigzag 

 line, often remaining stationary, tiU 5 p.m., ■when the great 

 evening fall commenced, which was continued till at least 

 10 P.M. By 7 A.M. on the following morning it had risen to the 

 same level as on the previous morning, and then descended in 

 a zigzag Hne. But from 10.30 a.m. till 4.15 p.m. it remained 

 almost motionless, all power of movement being now lost. The 

 petiole, therefore, of this very old leaf, which must have long 

 ceased growing, moved periodically ; but instead of circum- 

 nutating several times during the day, it moved only twice 

 down and twice up in the course of 24 h., with the ascending 

 and descending lines not coincident. 



It has already been stated that the pinnae move independently 

 of the main petiole. The petiole of a leaf was fixed to a cork 

 support, close to the point whence the four pinnse diverge, with 

 a short fine filament cemented longitudinally to one of the two 

 terminal pinnae, and a graduated semicircle was placed close 

 beneath it. By lookiug vertically down, its angular or lateral 

 movements could be measured with accuracy. Between noon 

 and 4.15 r m. the pinna changed its position to one side by only 

 7°; but not continuously in the same direction, as it moved 

 four times to one side, and three times to the opposite side. 



