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Show 386 MODIFIED CIRCUMNUTATION. CHAP, VII. Ipomrea crerulea andpurpurea (Convolvulacero). - The leaves on very young plants, a foot or two in height, arc depressed at night Fig. 163. to between 68° and 80° beneath the horizon· and some hang quit~ vertically downwards. On the following morning they again rise into a horizontal position. Tho petioles become at night downwardly curved, either through their entire length or in the upper part alone; and this apparently causes the depression of tho blade. It seems necessary that the leaves should be woll illuminated during the day in order to sleep, for those which stood on the back of a plant before a north-east window did not sleep. Nicot-iana tabacum B:1D'a:mnt!- (var. Virginian) and gla~tca (Solancre).-The young leaves of both these species sleep by bcndinh vertically up· wards. Figures of two shoots of N. glauca, 3•p.m.IJJI(o awake and asleep (Fig. Nicotiana tabacurn: circumnutatiou and nyc- 162), arc given on P· titropic movement of a leaf (5ij inches in 385 : one of the shoots, length), traced on a verti cal glass, from from which the photo- 3 P.M. Ju!v lOth to 8.10 A.M. 13th. Apex of leaf 4 inches from glass. Temp. 17 t0 - graphs were taken, was 18~° C. Figure reduced to one-half accidontallybenttoone original scale. side. At the base of the petiole of N. tabacum, on the outsibd e,e t haenrde is a mass of cells, which are rather smaller than clsew er' CHAP. VII. SLEEP OF LEA YES. 387 have ~heir longer axes differently directed from the cells of the parenchyma, and may therefore be considered as forming a sort of pulvinus. A young plant of N. tubacum was selected, and the circumnutation of the fifth loaf above the cotyledons was observed during three days. On the first morning (July lOth) the leaf fell from 9 to 10 A.M., which is its normal course, but rose during the remainder of the d(ty; and this no doubt was due to its being illuminated exclusively from above; for properly the evening rise does not commence until 3 or 4 P.M. In the figure as given on p. 386 (Fig. 163) tho first dot was made at 3 P.M.; and the tracing was continued for the following 65 h. Whentheleafpointed to the dot next above that marked 3 P.M., it stood horizontally. The tracing is remarkable only from its simplicity and the straightness of tho lines. The leaf each day described a single great ellipse ; for it should be observed that the ascending and descending lines do not coincide. On the evening of the 11th the leaf did not descend quite so low as usual, and it now zigzagged a little. The diurnal sinking move- . ment had already commenced each morning by 7 A.M. The broken lines at the top of the figure, representing the nocturnal vertical posit.ion ~~the l~af, ought to be prolonged much higher up. Mlrab1l~s longijlora and jalapa (Nyctaginero).-The first pair of leaves ~hove the cotyledons, produced by seedlings of both these speCies, were considerably divergent durino- the day and t . h b ' a rug t stood up vertically in close contact with one another. -~he two upper le~ves on an older seedling were almost horizontal Y day, an~ at mght stood up vertically, but were not in close contact, owmg to the resistance offered by the central bud. Polygtmum aviculare (Polygonero).-Profossor Batalin informs ~s th~t the young leaves rise up vertically at night. This is likeWise the case, according to Linnrous with several species of A h ' me marant. us (.A.maranthacere); and we obsm·ved a sleep move- 11 nt of this kind in one member of the genus. Again with v'heno.-vvl· lb ' 'l'v ... tu:n a um (Chenopodiere), the upper young leaves of ::e s~lmgs, about 4 inches in height, were horizontal or werehon.zontal during t~e day, ~nd at 10 P.M. on March 7th th qmte, or almost qUite, vert10al. Other seedlings raised in an~~enhouse duri~g the winter (Jan. 28th) were observed day of thn~ght, and no d1fference could be pe1·ceived in the position p. 3.;1 r leaves. According to Bouche (' Bot. Zeitung,' 187 4, sleeu )tth~ leaves of Pimelia linoides and spectabilis (Thymelero) Pa. rught. 2 c 2 |