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Show 238 CIRCUMNUTATION OF LEAVES. CHAP. IV. d On both days the leaf began to descend after 12 or 1 ay., 1 k 11nd continued to do so 11ll night, though to a 0 c oc ' < very unequal dist11nce on the Fig. 105. two occasionsll We therefore 'U'45'pJ! thought that the movement ! I 1o·4o'a.n~.s~1 was periodic; hut on observing throe otl1er loaveR during several successive days and nights, we founcl this to be an error; and tho case is given merely as 11 caution. On the third morning the above leaf occu pi eel 11lmost exactly the same position as on the first morning ; and the tentacles by this time had unfolded sufficiently to project at right angles to th8 blade or disc. The leaves as they grow older generally sink more :1nd. more downwards. Tho movement of an oldish leaf, the glands of which were still secreting freely, ~·as traced for 24 h., during wh1ch time it continued to sink a little in a slightly zigzag line. On the following morning, at D1·osm·a I'Otnndifoli•l: circumnutation 7 A.M., a drop Of a solution of young leaf, with filan;ent fixe~ of carbonate of ammonia (2 to back of blade, tmced from 9.1., r to 1 oz. of water) was A.M. June 7th to 8.30 A.M. June g · d' c and this 9th. Figure here reduced to one- placed on the IS ' nd in· half original scale. blackened the glands a tb t 1 The weight of 0 duced inflection of many of the ~en a\~:tle. but immediately drop caused the leaf at ~rst .to smk a h t ~irrzag course, and afterwards it began to r1so Ill a somew a. 0 tated about continued to do so t1'l l 3 It then cncumnu' P.M. 21 h . and during tho the same spot on a very small sc.ale for .j ' the same level next 21 h. it sank in a zigzag hne .to nearfi!st administered. which it had held when the ammoma w~s d the glands had By this time the tentacles had ro-expande '~n that an old lei rccovere d the 1 . r prop'"''l ' colour· · We thus learn CHAP. IV. DICOTYLEDONS. 239 circumnutates on a small scale, at least whilst absorbing carbonate of ammonia; for it is probable that this absorption may stimulate growth and thus re-cxcite circumnutation. Whether the rising of the glass filament which was attached to the back of the leaf, resulted from its margin becoming slightly inflected (as generally occurs), or from the rising of the petiole, was not ascertained. In order to learn whether the tentacles or gland-hearing hairs circumnutate, the back of lt young leaf, with the innermost tentacles as yet incurved, was firmly cemented with shellac to a flat stick driven into compact damp argillaceous saml. The plant was placed under a micro cope with the stage removed and with an eye-piece micrometer, of which each division equalled ~h of an inch. It should be stated that as the lep.ves grow older the tentacles of the exterior rows bend outwards and downwards, so as ultimately to become deflt:cted considerably beneath the horizon. A tentacle iu the second row from the margin was selected for observation and was found to be moving outwards at a rate of - of ~n inch in 500 20m., or rlo of inch in 1 h. 40 m.; but as it likewise moved from side to side to an extent of above 500 of inch, the movement was probably one of modified circumnutation. A tentacle ou an old leaf was next observed. in the same manner. In 15 m. after being placed under the microscope it had moved about -IToo of an inch. During the next 7~ h. it was looked at repeatedly, and during this whole time it moved only another Woo of an inch; and this small movement may have been due to the settling of the damp sand (on which the pbnt rested), though the sand bad been firmly pressed down. We may therefore conclude that the tentacles when old do not circumnutate · yet this tentacle was so sensitive, that in 23 seconds after it~ gland had been merely touched with a bit of raw meat it began to c 1 . . . , ur Inwards. This fact 1s of some importance as it appa-rently shows that the inflection of the tentacles from' the stimulus 0~ absorbed animal matter (and no doubt from that of contact Wlt~ any ?bject) is n?t due to modified circumnutation. tJt5t) Dwru:ea rnusctpttla (Droseraceoo).-It should be premised t he leaves at an early stage of their development have the :ok lobes pressed closely together. These are at first directed ~ towards the centre of the plant; but they gradually rise up ~~ 1Boon sta~d at right angles to the petiole, and ultimately in ar Y a straight line with it. A young loaf, which with the |