114 



backwards; the former in order to reach the earth, and 

 the latter to gain the air. Keep a young stalk in- 

 clined, its extremity will grow upwards. Bend the 

 branches of all sorts of plants; cause the inferior sur- 

 face of their leaves to turn towards the sky ; you will 

 soon perceive that ail these leaves will turn back again, 

 and resume their former position : which motion will 

 be executed with a quickness proportionate to the heat 

 of the sun, or supleness of the leaves. Sow different 

 kinds of seeds in a closet or cellar ; carry thither some 

 small twigs, having their extremity steeped in vessels 

 full of water ; the leaves of the young plants, and those 

 of the twigs, will incline their upper surface to the win- 

 dows or air-holes. 



Consider the leaves of divers species of herbaceous 

 plants ; of the mallow for instance : you will remark 

 that they follow the course of the sun. In the morning 

 you will see them present their upper surface to the 

 east ; towards the middle of the day this surface will 

 face the south ; in the evening it will be turned to the 

 west. At piglit, or in rainy weather, these leaves will 

 be horizontal, their inferior surface looking towards the 

 earth. 



Trace, likewise, the leaves of the acacia; as soen as 

 they are headed by the sun, you will observe all their 

 foliages draw together by their upper surface: they 

 will then form a kind of gutter, turned towards the 

 sun. In the night, or in moist weather, you will see 

 the foliage turned the contrary way, and contracting 

 themselves by treir inferior surface : they will then form 

 a gutter that \viii face the earth. 



4. Do not seek for circulation in plants: as they are 

 more sin;p e than animals, evtry thing in them is per- 

 formed with (ess apparatus. 



In the da>-timc-, the acuon of the heat on the leaves, 

 draws to them in abundance the nutritious juice. The 

 small excretory vessels that appear in the forms of glo- 



