THE WONDERS OF VEGETATION. 255 



the plant or from accidental causes. The leaves of 

 certain plants are endowed with a motion which may 

 be termed revolving, because it follows a regular 

 curve, and thus describes in the air a figure like a 

 cone. The tendrils of the bryony, and of our garden 

 cucumbers, are endowed with this perpetual motion, 

 the duration of which depends to some extent on the 

 temperature. These motions are not apparent, ex- 

 cept under close and minute examination. This is 

 not the case with the motions of the Desmodium 

 gyraus. In this plant the leaves consist of three 

 parts : a large terminal leaflet in the centre, and two 

 smaller ones, lateral, and springing from the base of 

 the former. Now, for the whole lifetime of the 

 plant, by day and by night, in wet or dry weather, in 

 the sun or in the shade, the lateral leaflets perform 

 incessant little jerks, not unlike those of the second- 

 hand of a watch ; one of these rises a little distance, 

 and at the same time the other sinks by as much ; 

 when the first sinks, the other rises, the motions 

 being thus alternate and regular. They are the more 

 rapid in proportion as heat and moisture in- 

 crease, and are most evident when the sun's rays 

 are striking upon the plant. In India, on the banks 

 of the Ganges, where the plant is in full vigor, it has 

 been observed that the leaflets perform sixty of these 

 jerks per minute, and furnish us thus, as it were, with 

 a genuine vegetable watch. The large leaf performs 

 similar movements, bat much more gently. This 

 plant was discovered in Bengal, by Mrs. Mouson, a 

 distinguished English botanist, who died during her 



