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Show 62 CIRCUMNUTATION OF SEEDLINGS. CHAP. I. inch in height, and consisted of a single internode bearing a bud on its summit. The apex described between 8.30 A.M. and 10.20 P.M. (i.e. during nearly 14 hours) a figure which would probably have consisted of 3~ ellipses, had not the stem been drawn to one side untill P.M., after which hour it moved backwards. On the following morning it was not far distant from the point whence it had first started. The actual amount of movement of the apex from side to side was very small, viz. about Ts-th of an inch. The seedling of which the movements are shown in Fig. 48, B, was U inch in height, and consisted of three internodes besides the bud on the summit. The figure, which was described during 10 h., apparently represents two irregular and unequal ellipses or circles. The actual amount of movement of the apex, in the line not in:fluenned hy the light., was ·11 of an inch, and in that thus influenced · 37 of an inch. With a seedling 2 inches in height it was obvious, even without the aid of any tracing, that the uppermost part of the stem bent successively to all points of the compass, like the stem of a twining plant. A little increase in the power of circumnutating and in the flexibility of the stem, would convert the common asparagus into a twining plant, as has occurred with one species in this genus, namely, A. scandens. Plwlrtris Ccmariensis (Gramineru).- With the Graminere the part which first rises above the ground has been called by some authors the pileole; and various views have been expressed on its homological nature. It is considered by some great authorities to be a cot)ledon, which term we will use without venturing to express any opinion on the suhject. * It consists in the present case of a slightly flattened reddish sheath, terminating upwards in a sharp white edge; it encloses a true green leaf, whi0h protrudes from the sheath through a slit-like orifice, close beneath and at right angles to the sharp edge on the summit. The sheath is not arched when it breaks through the ground. The movements of three rather old seedlings, about U inch in height, shortly before the protrusion of the leaves, were first traced. They were illuminated exclusively from above; for, tl.S will hereafter be shown, they are excessively sensitive to the * We are indebted to the Rev. this subject, together with re· G. Henslow for an abstract of the ferences. views which have been held on CHAP. I. PHALARIS. 63 action of light; and if any enters even temporarily on one side, they merely bend to this side in slightly zigzag lines. Of the three tracings one alone (Fig. 49) is here given. Had the observations been more frequent during the 12 h., two oval figures would have been described with their longer axes at right angles to one another. The actual amount of movement of the apex from side to side was about ·3 of an inch. The figures described by the other two seedlings resembled to a certain extent the one here Fig .. 49. given. L' A seedling which bad just broken through the ground and projected Phala.ris Canariensis: circumnuonly ...Lth of an inch above th tatwn of a cotyledon, with a 2o · . e mark placed below the apex, surface, was next observed m the traced on a horizontal glass, same manner as before. .It was from 8.35 A.M. Nov. 26th to necessary to clear away the earth 8.45 A.M. 2?th. M~vement of all d th dl' apex magmfied 7 times here ron~ e see mg to a little reduced to one-half seal~. depth m order to place a mark beneath the ape~. The figure (Fig. 50) shows that the apex moved to one s1de, but changed its course ten times in the course of the ten hours of observa-tion; so that there qan be no doubt Fig. 50. about its circumnutation. The cause of the general movement in one direction could hardly be attributed to the entrance of lateral light, as this was carefully ~arde~ against; and we suppose It was m some manner connected Plwlaris Canariensis: circumnu-with the removal of the earth tation of a very young coty-round the little seedling. ledon, with a mark placed Lastly, the soil in the same pot bel~w the apex, traced on a honzontal glass, from 11.37 was searched with the aid of a A.M. to 9.30 P.M. Dec. 13th. lens, and the white knife-like apex Movement of apex greatly of a seedling was found on an exact magnifi:d, here .. reduced to level with that of the surrouna ·m g one-fouith of ongmal scale. souf rface. Th. e so1'l :was r.e move d all round the apex to the depth :quarter of an mch, the seed itself remaining covered. The po , protected from lateral light, was placed under the micro- |
