654 PHYSIOLOGY. 



The epoch at which the movements take place is very varied. Ordi- 

 narily, leaves expand in the daylight and close towards evening 1 , while 

 flowers exhibit a great diversity of hahit in this respect so much so, 

 indeed, that Linnseus was enabled to draw up a list of flowers, fancifully 

 termed a " floral clock" (horologium Florce), in which a periodical move- 

 ment (opening or closing) marked each succeeding hour. 



Ipomcea Nil and Calystegia sepium open their flowers at 3-4 A.M. ; 

 Traaopogon at 3-4 A.M., closing again before noon ; some Nympluece, 

 Nuphar', Lactuca, &c., about 6 A.M. ; Anagallis arvensis, 8 A.M. (closing 

 again when the sky is overcast) ; Ornithogalum umbellatum, 11 A.M. ; Me- 

 sembryanthaceae generally about 12 ; Silene noctiflora, OEnothera biennis, 

 Mirabilis Jalapa, &c., 5-7 P.M. ; Cereus grandijlorus &c., Datura, Mesem- 

 bryanthemum noctiftorum, &c., 7-8 P.M. ; Victoria regia opens for the first 

 time about G P.M., and closes in a few hours, then opens again at 6 A.M. 

 the next day, remaining open until the afternoon, when it closes and sinks 

 below the water. 



Some closing flowers may be caused to open by exposure to strong arti- 

 ficial light (Crocus, Gentiana vernd) j on others (Convolvulus) this has no 

 effect. 



In most of the periodical movements the motion is very slow ; but certain 

 exceptions to this exist. Thus in the leaves of Desmodium gyrans and other 

 species, the labellum of M egaclinium falcatum, the styles of Stylidium adna- 

 tum, and others, the movement is quick enough to be directly perceptible. 



In Desmodium gyrans (the Telegraph-plant) the trifoliolate compound 

 leaf has a large terminal leaflet, and a smaller one on each side. When 

 this plant is exposed to bright sunlight, in a hothouse, the end leaflet 

 stands horizontally, and it falls downward in the evening ; but the lateral 

 leaflets move constantly during the heat of the day, advancing edge first 

 towards the end leaflet, and then retreating and moving towards the base 

 of the common petiole, alternately on each side, in a manner very well 

 compared to the movements of the arms of the old semaphore telegraphs. 

 In Megaclinium falcatum (Orchidacese), when exposed to sufficient heat, 

 the labellum rises and falls slowly in periods of several minutes; this 

 structure is also irritable, and moves more quickly, with an oscillatory 

 motion, when touched. 



Induced Movements. Irregular or irritable movements take place in a 

 great variety of plants, of which the following paragraph contains the 

 most striking examples, separately or in association with the spontaneous 

 movements before mentioned. They are influenced by contact and by 

 various chemical agents, while others paralyze the motion : 



Leaves : The " Sensitive Plants " (Mimosa pudica, sensitiva, casta, and 

 manv other species) ; AZschynomene sensitiva, indica, pumila Smithia 

 sensitiva; Desmanthus stolonifer, triquetris, lacustris; Oxalis sensitiva, and, 

 in less degree, Oxalis stricta, Acetosella,corniculata, Deppei, &c. ; Robinia 

 Pseudoacacia folds its leaves when violently shaken in the morning; 

 lastly Dioncea muscipula, the Venus's Fly-trap, which folds its leaves 

 when visited by insects, and Drosera (fig. 588, p. 560), which enfolds itself 

 over the captured prey. 



The spontaneous slow movement which occurs at stated periods (move- 

 ments of sleeping and waking) is, as has been said, different from the 

 sudden motion caused by external stimuli. Ether and other anaesthetics 





