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Show 384 l\IODIFIED CIRCUMNUTA'l'ION. C HAP. VII. leaf hacl rison greatly, and continued to rise till 7.50 A.M., after which hour it rodoscenclod. It should be observed that tho lines traced on this second morning would have coincided with and confused those previously traced, had not the pot been slidcd a very little to the loft. In tho evening (14th) a mark wa, placed behind the filament attached to tho apex of tho leaf, and its movement was carefully traced from 5 l>.M. t,o 10.15 u. Fig. 161. ·--..•... ) Passlflora gr,!cilis: circumnutation and n ycti trop~c movement of 1~ct:· traced on vertical glass, from 8.20 A.M. Oct. 10th to 10 A. ~l. · Figul'e reduced to two-thirds of original scale. Between 5 and 7.15 P.M. the loaf descended in a straight linct and at the latter hour it appeared vertically dependent. ~u between 7.15 ancl 10.15 P.M. the line consisted of a snc~c 81011 of steps the cause of which we could not understand; 1~ was, however', mam.f est that tho movomon t was no 1o n gcr a s1mple d·escending one. . ell' were Siegesbeclcia orientalis (Compos1tro).-Some sec mgs raised in the middle of winter and kept in tho hot-honsel; thcdy :flowered, but did not grow well, and thm.r 1e ~vos no.v er sin J OMWCa y any signs of sleep Tho leaves on other sccdlmgs raised . wcre horizontal a·t noon (June 22nd), an d d open de c 1 at a con 1- CnAP. VII. SLEEP OF LEAVES. 385 deraole angle beneath the horizon at 10 P.M. In the case of fonr youngish loaves, which were from 2 to 2.t inches in length, these angles were found to bo 50°, 56°, 60°, and 65°. At tho end of August, when the plants had grown to a height of 10 to l1 inches, tho younger leaves were so much curved downwards at night that they might truly be said to bo asleep. This is one Fig. 16::3. Nicotiana gl~11ca: sh_oots with leaves expanded during the day, and asleep at mght. F1gures copied from photographs, and reduced. ~f the species which must be well illuminated during tho day In orde~ to sleep, for on two occasions when plants were kept aU day m a room with north-east windows, the leaves did not ~leep at night. Tho same cause probably accounts for the ~v~ on our seedlings raised in the clead of the winter not 800 Ping. Professor Pfeffer informs us that the leaves of llllothet species (B. Jorulltnsis ?) hang vertically clown at night. 2 c |
