CHAP. VII SUMMARY ON SLEEP OF LEAVES. 411 



until the evening. If the reader will lock, for in- 

 stance, at the diagram (Fig. 142, p. 351), representing 

 the nyctitropic movements of the terminal leaflet of 

 Trifolium subterraneum, remembering that the curved 

 broken lines at the top ought to be prolonged much 

 higher up, he will see that the great rise in the evening 

 and the great fall in the morning together form a 

 large ellipse like one of those described during the 

 daytime, differing only in size. Or, he may look at 

 the diagram (Fig. 103, p. 236) of the 3 ellipses 

 described in the course of 6 h. 35 m. by a leaf of 

 Lupinus speciosus, which is one of the species in this 

 genus that does not sleep ; and he will see that by 

 merely prolonging upwards the line which was already 

 rising late in the evening, and bringing it down 

 again next morning, the diagram would represent the 

 movements of a sleeping plant. 



With those sleeping plants which describe several 

 ellipses in the daytime, and which travel in a strongly 

 zigzag line, often making in their course minute loops, 

 triangles, &c., if as soon as one of the ellipses begins 

 in the evening to be greatly increased in size, dots are 

 made every 2 or 3 minutes and these are joined, the 

 line then described is almost strictly rectilinear, in 

 strong contrast with the lines made during the day- 

 time. This was observed with Desmodium gyrans and 

 Mimosa pudica. With this latter plant, moreover, the 

 pinna3 converge in the evening by a steady move- 

 ment, whereas during the day they are continually, 

 converging and diverging to a slight extent. In all 

 such cases it was scarcely possible to observe the 

 difference in the movement during the day and even- 

 ing, without being convinced that in the evening the 

 plant saves the expenditure of force by not moving 

 laterally, and that its whole energy is now expended 



