r90 



PHYSIOLOGY, 



those of certain leaves, and the petals of flowers, >^hich occur 

 at particular hours, and Avhich remain in the new position thus 

 taken up until the return of a particular period, when they re- 

 sume as nearly as possible their original position. In leaves, 

 these periodical movements consist in the closing up of such 

 organs towards the evening and their expansion in the daylight. 

 In the petals of flowers great differences occur in different 

 plants, some opening or closing at particular hours of the day; 

 and thus, by observing these changes in a variety of flowers, 

 Linnaeus and others have drawn up what has been termed a 

 floral clock. This periodical closing up of leaves and flowers has 

 been called the sleep of plants. The compound leaves of 

 certain Leguminosse and Oxalidacere are marked illustrations 

 of these periodical movements. All the above movements are 

 indirectly dependent upon the varying conditions of light to 

 which the parts of the plant in which they are found are exposed. 

 b. Not periodical. — Such movements are exhil)itedin a num- 

 ber of plants both in the leaves and in their reproductive organs. 

 In the leaves they are well seen in certain species of Oralis, 



Mimosa {fig. 350), in Dioncea 

 muscipula {fig. 352), &c. In 

 the Reproductive Organs they 

 may be noticed in the curving 

 inwards or outwards of the 

 stamens of certain plants, such 

 as those of Berberis vulgaris 

 and other species, Parietaria 

 judaica, Helianthemum vulgare 

 and other Cistacex ; also in 

 the stigmas of the Lobeliaceae, 

 &c. ; and in the style of Gold- 

 fussia anisophylla, ^c. All 

 the above movements are pro- 

 duced by external agency, 

 such as the action of insects, 

 the agitation caused by the 

 wind, &c.; and the immediate 

 object of such movements is 

 evidently to bring the pollen 

 into connection with the 

 stigma. 



2. Movements indepen- 

 dent, AT LEAST TO SOME EX- 

 TENT, OP EXTERNAL INFLU- 

 ENCES.— O. Periodical. — These 

 movements arc seen in the 

 leaflets of certain tropical species of Desmodium {Hedysarum), 

 iind more especially in those of Desmodium gyrans {fig. 1119). 



Fig. 1119. A portion of a branch, and the 

 ivaf of Desmodium gi/rans. The leaf is 

 trifoliate, and coiisistB of a large 

 terminal leaflet, n, and two smaller 

 ones. Ii. There are two other rudimen- 

 tary leiiflctH. marked also h. near the 

 tcrminul leaflet, hence the leaf would be 

 perhaps better characterised as inipari- 

 ])iniuite. 



