392 



MODIFIED CIEOUMNUTATION. 



Chap. VII 



On the second day the descending line zigzagged slightly. As 

 Pig ig5_ usual, the ascending and de- 



scending lines did not coincide. 

 On another occasion, when the 

 temperature was a little higher, 

 viz., 24°-26i° C, a leaf was 

 observed 17 times between 8.50 

 A.M. and 12.16 p.m. ; it changed 

 its course by as much as a 

 rectangle six times in- this in- 

 terval of 3 h. 26 m., and de- 

 .scribed two irregular triangles 

 and a half. The leaf, therefore, 

 on this occasion circumnutated 

 jrapidly and in a complex 

 manner. 



ACOTYLEDONS. 



Marsilea quadrifoliala (Mar- 

 sileaceie). — The shape of a leaf, 

 expanded horizontally during 

 the day, is shown at A (Kg. 166). 

 Each leaflet is provided with 

 a well-developed pulvrnus. 

 When the leaves sleep, the two 

 terminal leaflets rise up, twist 

 half round and come into con- 

 tact with one another (B), and 

 are afterwards embraced by the 

 two lower leaflets (0); so that 

 the four leaflets with their lower 

 surfaces turned outwards form 

 a vertical packet. The curva- 

 ture of the summit of the petiole 

 of the leaf figured asleep, is 

 merely accidental. The plant 

 was brought into a room, where 

 the temperature was only a little 

 above 60° P., and the movement 

 of one of the leaflets (the petiole 

 having been secured) was traced 



Strephmm florUiundum : circumnii- 

 tation and nyctitvopic movement 

 of a leaf, traced from 9 A.M. June 

 26th to 8.45 A.M. 27th ; filament 

 fixed along the midrib. Apex of 

 leaf 8J inches from the vertical 

 glass ; plant illuminated from 

 above. Temp. 2.3J°-24|° C. 



