under surface of leaves, were covered, after some time, with 

 drops of dew, while they were little or not at all stained when 

 they were fastened to the upper surface. 



314. 



Generally the leaves, and leafy integuments, are the or- 

 gans, which, by exhalation and absorption, like the breathing 

 organs of animals, maintain the proper composition of the 

 plant, and contribute essentially to nourishment and propa- 

 gation. 



Experiments and observations have instructed us, that 

 healthy and green leaves, during sunshine, take in carbonic 

 acid, and give out oxvgen in the state of gas. In the shade, 

 and at night, as also when they are sickly and take a differ- 

 ent colour from the green, they take in oxygen gas, and give 

 out carbonic acid. By these two functions, however, the 

 condition of the atmosphere is not to any great extent alter- 

 ed, either with respect to its quantity of oxygen, or of car- 

 bonic acid. Let us then enclose the green parts of vegetables 

 in a definite portion of air. In this case the quantity of oxy- 

 gen, during sunshine, is increased to such an extent, that 

 from twelve square inches of green blades, ten cubic inches of 

 oxygen are produced in a few minutes. The increase of car- 

 bonic acid from plants, which are confined in the shade, may 

 also be observed from the resolution of lime-water placed in 

 a similar confined space. In the open air, on the contrary, 

 scarcely more than the usual quantity of oxygen is imparted, 

 by this means, to the atmosphere, because it is impossible 

 that all the lea\es can be at the same time illuminated by the 

 sun ; for in bushes, forests, and gardens, a greater pro|X)r- 

 tion of leaves is always in shade, and, consequently, by the 

 production of carbonic acid, the quantity of oxygen giis is 

 balanced. It thus happens that the produced oxygen is 

 constantly consumed^ as well by the shaded leaves as by 

 animals, and also by the soil, which is incessantly taking 

 it up. It maintains an equality with the carbonic acid given 

 out in the shade. This carbonic acid is constantly deposited, 

 during the night, along with liic dc\v : jnul dnrin<; ^\ui-]iin(\ 



