Chap. IV. DICOTYLEDONS. 239 



circumnutates on a small scale, at least wliilst absorbing car- 

 bonate of ammonia ; for it is probable that this absorption may 

 stimulate growth and thus re-excite 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 

 ivscertained. 



In order to learn whether the tentacles or gland-bearing hairs 

 circumnutate, the back of a yonng leaf, with the innermost 

 tentacles as yet incurved, was firmly cemented with shellac 

 to a flat stick driven into compact damp argillaceous sand. 

 The plant was placed under a microscope with ihe stage re- 

 moved and with an eye- piece micrometer, of which each 

 division equalled -5^ of an inch. It should be stated that as 

 the leaves grow older the tentacles of the exterior rows bend 

 outwards and downwards, so as ultimately to become deflected 

 considerably beneath the horizon. A ttntacle in the second 

 row from the margin was selected for observation, and was 

 found to be moving outwards at a rate of 5 J^ of an inch in 

 20 m., or y^ of inch in 1 h. 40 m. ; but as it likewise moved 

 from side to side to an extent of above 5^ of inch, the move- 

 ment was probably one of modified circumnutation. A tentacle 

 on an old leaf was next observed in the same manner. In 

 15 m. after being placed under the microscope it had moved 

 about Yj^o of an inch. During the next 72 h. it was looked at 

 repeatedly, and during this whole time it moved only another 

 Y^ of an inch ; and this small movement may have been due 

 to the settling of the damp sand (on which the plant rested), 

 though the sand had been firmly pressed down. We may there- 

 fore conclude that the tentacles when old do not circumnutate ; 

 yet this tentacle was so sensitive, that in 23 seconds after its 

 gland had been merely touched with a bit of raw meat, it began 

 to curl inwai'ds. This fact is of some importance, as it appa- 

 rently shows that the inflection of the tentacles from the stimulus 

 of absorbed animal matter (and no doubt from that of contact 

 with any object) is not due to modified circumnutation. 



(15.) Dioiicea mmcipi-la (Droseraceas). — It should be premised 

 that the leaves at an early stage of their development have the 

 two lobes pressed closely together. These are at first directed 

 back towards the centre of the plant ; but they gradually rise up 

 and soon stand at right angles to the petiole, and ultimately in 

 nearly a straight line with it. A young leaf, which with t,h« 



