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Show 370 MODIFIED CIRCUl\:1NUTA'l'ION. CHAP. VII. sink downwards and rotate, so that they stand laterally at night, as may be seen in the figure. Moreover, they move soruewhnt backwards, so as to point towards the base of tho petiole. Fig. 154. Cassia corymbosa: A, plant during day; B, same plant at night. Both figures copied from photographs. In one instance we found that the m1·c 1 n · 1 J of 'a tormin:1Jl leaflet formed at night an angle of 36°, with a line droppc CuAP. VII. SLEEP OF LEAVES. 371 perpendicularly from the end of tho petiole. The second pair ofleaflets likewise moves a little backwards, but less than tho terminal pair; and the third pair moves vertically down wards, or even a little forwards. Thus all the leaflets, in those specjos which bear only 3 or 4 pairs, tend to form a single packet, with their upper surfaces in contact, and their lower surfaces turned outwards. Lastly, tho main petiole rises at night, but with leaves of different ages to very different degrees, namely, some rose through an angle of only 12°, and others as much as 41°. Ca.~sia calliantha.-The loaves bear a large number of leaflets which move at night in nearly tho same manner as just described; but the petioles apparently do not rise, and one which was carefully observed certainly fell 3°. Cassia pubescens.- The chief difference in the nyctitropic Fig. 155, B. ___,__ \ Cauia pub escens:. A, uppe~ part of plant during the day; B, same plant at l1lght. F1gures reduced from photographs. !:~menta of this species, compared with those of the former "l"'''468 co . t . ' ns1s s m the leaflets not rotating nearly so much; 2 B 2 |