OCR Text |
Show 42 CIRCUMNUTATION OF SEEDLINGS. CHAP. I. cotyledon fell; it then rose rapidly till 9. P.M., the:1 very gradually till 3 A.M. February 19th, after which hour It sank gradually till 4.30 P.M.; but the downward movement was int.errupted by one slight rise or oscillat~on about ~.30 P.M •. After 4.30 P.M. (19th) the cotyledon rose till 1 A.M. (m .the mght of February 20th) and then sank very gradually till 9.30 A.M., when our observations ceased. The amount of movement 1vas greater on the 18th than on the 19th or on the morning of the 20th. Oucurbita aumrdia.-An arched hypocotyl was found buried a little beneath the surface of the soil; and in order to prevent it straightening itself quickly, when relieved from the surrounding pressure of the soil, the two legs of the arch were tied together. The seed was then lightly covered with loose dn.mp earth. A filament with a bead at the end was affixed to the basal leg, the movements of which were observed during two days in tho usual manner. On the first day the arch moved in a zigzag line towards the side of the basal leg. On the next day, by which time the dependent cotyledons had been dragged above the surface of the soil, the tied arch changed its course greatly nine times in the course of 14! b. It swept a large, extremely irregular, circular figure, returning at night to nearly the same spot whence it had started early in the moming. 'l'he line was so strongly zigzag that it apparently represented five ellipses, with their longer axes pointing in various directions. With respect to the periodical movements of the cotyledons, those of several young seedlings formed together at 4 P.M. an angle of about 60°, and at 10 P.M. their lower parts stood vertically and were in contact; their tips, however, as is usual in the genus, were permanently re:fl.exed. These cotyledons, at 7 A.M. on the following morning, were again well expanded. Lagena1·ia vulgaris (var. miniature Bottle-gourd) (Cucurbitacere).- A seedling opened its cotyledons, the movements of which were alone observed, slightly on June 27th, and closed them at night: next day, at noon (28th), they included an angle of 53°, and at lO'F.M. they were in close contact, so that each had risen 26~ 0 • At noon, on the 29th, they included an angle of ll8°, and at 10 P.M. an angle of 54°, SO each had risen 32°. On the following day they were still more open, and the nocturnal rise was greater, but the angles were not measured. Two other seedlings wei·e observed, and behaved during three days in a closely similar manner. rrhe cotyledons, therefore, CHAP. I. CUCURBITA. 43 open more and more on each succeeding day, and rise each night about 30°; consequently during the first two nights of their life they stand vertically and come into contact. In Ol'der to ascertain more accurately the nature of those movements, the hypocotyl of a seedling, with its cotyledons well expanded, was secured to a little stick and a filament with triangles of' paper was atllxed to one of the cotyledons. The observations were made under a rather dim skylight, and the temperature during the whole time was l>etwocn 17 ~ 0 to u~o c. ((:53° to 65° F.). Had the temperature been higher and the light brighter, the movements would probably have b~en greater. On July 11th (see F1g. 30), the cotyledon fell from 7.35 A.M. till 10 A.M.; it then rose (rapidly after 4 P.M.) till it stood quito vertically at 8.40 P.M. During the early morning of the next day (12th) it fell, and continued to fall till 8 A.M., after which hour it rose then fell, and again rose, so that b; 10.35 P.M. it stood much higher than it did in the morning, but was not vertical as on the preceding night. During the following early morning and whole clay (13th) it fell and circumnutated, but had not risen when o?served late in the evening; and th1s was probably due to the deficiency of heat or light, or of both. We thus see that the cotyledons became more widely open at noon on each succeeding day ; and Fig. 30. {\ ! 1 r.o1:;'p.nt., f 11 ~!· ! 20 1.J!O wo:w'p.m:: go~'a.m. 13~1£ \t H:t:k La,qenw·ia vulgttris: circumnu~ atio~ of a cotyledon, 1! ~nch Ill length, apex only 4~ mches from the vertical glass on which its movements wer; traced from 7.35 A.M. July 11th to 9.5 A.M. on the 14th. Figure here given reduceu to one-third of original scale. that ~hey ro~e. considerably each night, though not acquiring a v~rtiCal. pos1t10~, except d~ring the first two nights. Gucumu; dudu~m (Cucurbitacere).-Two seedlings had opened |