CHAP. VII. SUMMARY ON SLEEP OF LEAVES. 405 



day, and two on the next. Erythrina corallodendron 

 made four ellipses on the first day of observation 

 and only a single one on the third, apparently owing 

 to having been kept not sufficiently illuminated and 

 perhaps not warm enough. But there seems likewise 

 to be an innate tendency in different species of the 

 same genus to make a different number of ellipses in 

 the twenty-four hours : the leaflets of Trifolium repens 

 made only one ; those of T. resupinatum two, and those 

 of T. subterraneum three in this time. Again, the 

 leaflets of Oxalis Plumierii made a single ellipse ; those 

 of 0. lupleurifolia, two ; those of 0. Valdiviana, two or 

 three ; and those of 0. acetosella, at least five in the 

 twenty-four hours. 



The line followed by the apex of a leaf or leaflet, 

 whilst describing one or more ellipses during the day, 

 is often zigzag, either throughout its whole course or 

 only during the morning or evening : Robinia offered 

 an instance of zigzagging confined to the morning, 

 and a similar movement in the evening is shown in 

 the diagram (Fig. 126) given under Sida. The amount 

 of the zigzag movement depends largely on the plant 

 being placed under highly favourable conditions. But 

 even under such favourable conditions, if the dots which 

 mark the position of the apex are made at consider- 

 able intervals of time, and the dots are then joined, 

 the course pursued will still appear comparatively 

 simple, although the number of the ellipses will be 

 increased; but if dots are made every two or three 

 minutes and these are joined, the result often is that 

 all the lines are strongly zigzag, many small loops, 

 triangles, and other figures being also formed. This 

 fact is shown in two parts of the diagram (Fig. 150) 

 of the movements of Desmodium gyrans. Strephium 

 Jloribundum, observed under a high temperature, 



