OF NATURAL HISTORY. 7 



felves fo as to give the beft protedtlon to the young ftems, flowers, 

 buds, or fruit. The leaves of the tamarind- tree contrafl: round the 

 tender fruit, and proteft it from the nodurnal cold. The caffia or 

 fenna, the glycine, and many of the papilionaceous plants, contract 

 their leaves in a fimilar manner. The leaves of the chickweed, of 

 the afclepias, atriplex, &c. arc difpofed in oppofite pairs. During 

 the night, they rife perpendicularly, and join fo clofe at the top, 

 that they conceal the flowers. The leaves of the fida or althaea 

 Theophrafli, of the ayenia, and Oenothera, are placed alternately. 

 Though horizonal, or even depending, during the day, at the ap- 

 proach of night they rife, embrace the flem, and protefl: the tender 

 flowers. The leaves of the folanum, or nightfhade, are hori- 

 zontal during the day ; but, in the night, they rife and cover the 

 flowers. The Egyptian vetch ereds its leaves during the night, in 

 fuch a manner that each pair feem to be one leaf only. The leaves 

 of the white lupine, in the ftate of fleep, hang down, and prote<5l 

 the young buds from being injured by the nodturnal air. 



Thefe and fimilar motions are not peculiar to the leaves of plants. 

 The flowers have alfo the power of moving. During the night, 

 many of them are inclofed in their calixes. Some flowers, as thofe 

 of the German fpurge, geranium ftriatum, and common whitlow 

 grafs, when afleep, hang their mouths toward the earth, to prevent 

 the noxious effects of rain or dew. 



The caufe of thofe movements which conftitute the fleep of plants, 

 has been afcribed to the prefence or abfence of the fun's rays. In 

 fome of the examples I have given, the motions produced are evi- 

 dently excited by heat. But plants kept in a hot-houfe, where an 

 equal degree of heat is preferved both day and night, fail not to 

 contract their leaves, or to fleep, in the fame manner as when they 

 are expofed to the open air. This fad evinces, that the fleep of 



plants 



