IS THE PHILOSOPHY 



ceive that all thefe leaves refiime their original pofition. 

 Thefe motions are performed fooner or later, in proportion 

 to the degree of heat, and the flexibility of the leaves. 

 Many leaves, as thofe of the mallow, follow the courfe of the 

 fun. In the morning, their fuperior furfaces are prefented 

 to the eaft ; at noon, they regard the fouth ; and, when the 

 fun fets, they are directed to the weft. During the night, 

 or in rainy weather, thefe leaves are horizontal 5 and their 

 inferior furfaces are turned toward the earth. 



What has been denominated the fleep of plants, affords an 

 Inflance of another fpecies of vegetable motion. The leaves 

 of many plants fold up during the night ; but at the ap- 

 proach of the fun, they expand with renewed vigour. The 

 common appearances of moft vegetables are fo changed in 

 the night, that it is difficult to recognize the different kinds, 

 even by the afliflance of light. 



The modes of folding in the leaves, or of fleeping, are ex- 

 tremely various. But it is worthy of remark, that they all 

 difpofe themfelves fo as to give the beft proteftion to the 

 young ftems, flowers, buds, or fruit. The leaves of the tam- 

 arind tree contradl round the tender fruit, and protect It 

 from the no£lurnal cold. The caffia or fenna, the glycine, 

 and many of the papilionaceous plants, contract their leaves 

 in a flmilar manner. The leaves of the chickweed, of 

 the afclepias, atriplex, &c. are difpofed in oppoilte 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 althea theophrifti, of the ayenia, and 

 Oenothera, are placed alternately. Though horizonal, or 

 even depending, during the day, at the approach of night 

 they rife, embrace the ftem, and prote(Sl the tender flowers. 

 The leaves of the folanum, or nightfliade, are horizontal du- 

 ring the day •, but, in the night, they rife and cover the 

 lowers. The Egyptian vetch ere^s its leaves during the 



