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Show 302 l\IODIFIED CIRCUl\fNU'l'A.TIO~. CIIA.P. VI. the petioles diverged before it was light. The hypocotyl is slightly sensitive, so that if rubbed with a needle it bends towards the rubbed . ide. In the case of J. epidiwn sativum, the petioles of the cotyledons of young seedlings diverge during the day and converge so as to touch each other during the night, by which means the bases of the tripartite blades are brought into contact; but the blades are so little raised that they cannot be said to sleep. Tho cotyledons of several other Cl'Uciferous plants mn·e ohservecl, but they did not rise sufficiently during the night to be said to sloop. Githago sl!getum (Caryophyllcro).-On the first day after the cotyledons had burst through the seed-coats, they stood at noon at an angle of 75° above the horizon ; at night they moved upwards, each through an angle of 15° so as to stancl quite vertical and in contact with one another. On the second day they stood at noon at 59° above the horizon, and again at night were completely closed, each having risen 31°. On the fourth clay the cotylcclons did not quite clo e at night. The first and succeeding pairs of young true leaves behaved in exact.ly the same manner. We think that the movement in this case may be callccl nyctitropic, though tho angle passed through 'iVa~ small. The cotyledons are very sensitive to light aud will not expand if exposed to an extremely dim one. ~~node£ W1·ightii (Malvaccro).-Thc otyledons whilst moderately young, 'and only from ·2 to ·3 i.nch in dia~1~ter, sink in .tl!~ eveninO' from their mid-day hol'lzontal positiOn to about 3o beneath the horizon. But when tho same seedlings were older and had produced small true loaves, the almost orbicular cotyledons, now ·55 inch in diameter, move l vertically dow uw~rds at night. This fact made us suspect that their sinl.cing nught be due merely to their weight; hut they wore not. m_tl~c l~ast flaccid, and when lifted up sprang back through elastJCJty .mto their former dependent po. ition. A pot with some old seedlmgs was turned upside down in the afternoon, before the. noc· turnal fall had commenced, and at night they assumed. mop· position to their own weight (and to any geotropic aetwu) an upwardly directed vertical position. When pots were th~s reversed after the evening fall had already commenced, t te sm. km. g m' ovement appeared to be somew h a t dI'S t m· bed·• but all their movements were occasionally variable without any apparent cause. Thi.s latter fact, as well as that of the young cotyledo.n s not sinking nearly so much as the older ones, de sc rves notwe. CHAI'. VI. SLEEP OF COTYLEDONS. 303 Although the movement of tho cotyledons endured for a long time, no pulvinus was exteriorly visible; but their growth continued for a long time. The cotyledons appear to be only slightly heliotropic, though the hypocotyl is strongly so. Gossypiumarbor·eum (?) (var. Nankin cotton) (Malvacere).-The cotyledons behave in nearly the same manner as those of the Anoda. On June 15th tho cotyledons of two seedlings were ·65 inch in length (measured along the midrib) and stood horizontally at noon; at 10 P.M. they occupied the same position and had not fallen at all. On June 23rd, the cotyledons of one of these seedlings were 1·1 inch in length, and by 10 P.M. they had fallen from a horizontal position to 62° beneath the horizon. The. cotyledons of the other seedling were 1·3 inch in length, and ammute true leaf had been formed; they had fallen at 10 P.M. to 70° beneath the horizon. On June 25th, the true leaf of this latter seedling was ·9 inch in length, and the cotyledons occupied nearly the same position at night. By July 9th the cotyledons appeared very old and showed signs of withering; but they stood at noon almost horizontally, and at 10 P.l\l. hung down vertically. .Gossyp.ium hf'rb· tceum.-It is remarkable that tho cotyledons of this speCies behave differently from those of tho last. They were observed during 6 weeks from their first development until they had. gro~ to a very large size (still appearing fresh and green), VIZ. 2! mches in breadth. At this age a true leaf had been formed, which. with its petiole ·was 2 inches lo11g. During the whole of thes~ G ~ecks the cotyledons did not sink at night; yet when old thmr wmght was considerable and they were borne by much elongated petioles. Seedlings raised from some seed ~ent ~from N~ples, ~ohavcd in the same manner; as did those fa kmd cu~tivated m Alabama and of tho Sea-island cotton. Towhat speCies these three latter forms belong we do not know. i:e cou~~ not make out in the ca e of the Naples cotton, that ~ po~Ihon of the cotyledons at night wo.s influenced by tho soil bemg more or less dry ; care being taken that they were not rendered flaccid by being too dq. 'l'he weio·ht of tbe larcre ~tyledons of the Alabama and Sea-island kinds °Caused them to ang somewhat downwards, when the pots in which they gTow Were left fo t' · b r a 1me upside down. It should however bo oth serv.e d th a t the se three ki·n ds were raised in ' the middl'e of n '~ti~m~r, which sometimes greatly interferes with the proper J ropiC movements of leaves and cotyledons. .. ;, ,... ,, II |