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Show MODIFIED CIRCUMNUTATION. GIIAP. X. upright flower-heads, arising from branches in all sorts of positions, on plants growing in a warm greenhouse, were marked with thread, and after 24 h. six of them wore vertically dependent; these therefore had travelled through 180° in this time. Ton were extended sub-horizontally, and theRe hau moved through about 90°. Throe very young peduncles had as yet mo,od only a little downwards, but after an additional 24.h. were grea.tly inclined. At the time when tho flower-heads roach the ground, the younger imperfect flowers in the centre arc still prossed closely together, and form a conical projection; whereas the perfect and imperfect flowers on the outside arc upturned and closely surround the peduncle. They arc thus adapted to offer as little resistance, as the case admits of, in penetrating the ground, though the diameter of tho flower-head is still considerable. The means by which this penetration is effected will presently be described. The flower-heads a.re able to bury themselves in common garden moulci, and easily in sand or in fine sifted cinders packed rather closely. The depth to which they penetrated, measured from the surface to the base of tho head, was between i and ~ inch, but in one case rather above 0·6 inch. With a plant kept in the house, a bead partly buried itself in sand in 6 h. : after 3 days only the tips of the rcfl.cxed calyces were visible, and after 6 days the whole had disappeared. Dut with plants growing out of doors we believe, from casual observations, that they bury themselves in a much shorter time. After the heads have buried themselves, the central aborted flowers increase considerably in length and rigidity, and become bleached. They gradually curve, one after tho other, upwards or towards the peduncle, in tho same manner as did the perfect flowers at :first. In thus moving, the long claws on their summitB carry with them some earth. Hence a flowerhead which has been buried for a sufficient time, forms a rather large ball, consisting of tho a.borted flowers, separated from one another by earth, and surrounding the little pods (the product of the perfect flowers) which lie close round the upper part of the peduncle. The calyces of the perfect and imperfect flowers are clothed with simple and multicellular hairs, which have the power of absorption; for when placed in a weak so~ution of carbonate of ammonia (2 gr. to 1 oz. of water) thmr protoplasmic contents immediately became aggregated and afterwards displayed the usual slow movements. This clover generally CnAP. X. GEOTROPISM. 515 grows in dry soil, but whether tho power of absorption by the hairs on the buried flower-heads is of any importance to them we do not know. Only a few of tho flower-heads, which from their position are not able to reach the ground and bury themselves, yield seeds; whereas tho buried ones never failed, as far as we observed, to produce as many seeds as there had been perfect flowers. . We will now consider tho movements of the peduncle whilst Fig. 190. .25'!t Trifolium su_~terraneum: downward movement of peduncle from 19° beneath the horizon to a nearly ve1·tically dependent position, traced from II A.M. July 22nd to the morning of 25th. Glass filament fixed , .transversely across peduncle, at base of flower-head. e . d Fu:vm,g own to the ground. We have seen in Chap. IV., Ig. 92, p. 225, that an upright young flower-head circumnu- !ated . th conspiCuously; and that this movement continued after 6 peduncle had begun to bend downwards. 1'he same ~uncl~ was observed when inclined at an angle of 19° above t 6 hor1zon, and it circumnutated during two days. Another 2 L 2 |