MOVEMENTS OF PLANTS. 791 



The leaf in this plant is trifoliate, the terminal leaflet, a, 

 being much larger than the two lateral leaflets, b. The 

 large terminal leaflet, a, when exposed to the influence of a 

 bright light, becomes more or less horizontal, but it falls 

 downwards on the approach of evening. Such movements 

 are therefore clearly analogous to the sleep of plants pre- 

 viously described. The lateral leaflets, h, exhibit a con- 

 stant movement during the heat of the day, advancing by 

 their edges towards the large terminal leaflet and then 

 retreating towards the base of the common petiole. This 

 movement takes place first on one side and then on the 

 other, so that the point of each leaflet describes a circle. 

 These movements resemble those of the arms of the old 

 semaphore telegraphs, and hence this plant has been termed 

 the Telegraph plant. These movements go on to a less 

 extent even in the dark. They are most evident when the 

 plants are in a vigorous state of growth, and when exposed 

 to a high temperature. No satisfactory explanation has as yet 

 been given of the direct cause of this movement. 



b. Not periodical. — These movements occur in the repro- 

 ductive organs of a large number of the Phanerogamia, and their 

 object is clearly to transfer the pollen to the stigma. The stamens 

 sometimes curve inwards separately towards the stigma, as in 

 Huta graveolens {fig. 596), and Parnassia palustris ; or in pairs, 

 as in Saxifraga tridactylites. After the pollen is discharged, the 

 stamens commonly return as nearly as possible to their former 

 position. In Passiflora, Nigella sativa, certain Onagraceae and 

 Cacti, &c., the styles move to the stamens; while in other 

 Onagraceae and certain Malvaceae, &c., both styles and sta- 

 mens move towards each other. No explanation of a satis- 

 factory nature has been given of the cause of these movements. 



