166 ON VEGETABLE RESPIRATION'. 



shine, and found that the air which it contained in solution yielded 

 from 80 to 90 parts of oxygen ; whilst the water of the same sea, 

 collected in cloudy weather, did not contain more than from 16 to 

 17 per cent, of this gas. This enoraious difference sufficiently 

 accounts for the languor of the fish when unable to obtain their 

 accustomed supply of oxygen, and the increase of this precious 

 gas on the sunny days, those joyful days for the finny tribe, can 

 only be attributed to the influence of the marine vegetables, whose 

 respiration, stimulated by the presence of the sun, purifies the water 

 by diffusing a larger quantity of oxygen. But this isolated fact, 

 however curious, is no sufficient ground on which to establish that 

 constant relation between the animal and vegetable; kingdoms so 

 much insisted on by physiologists, which places them, as one may say, 

 in a state of mutual dependence ; giving to the animal kingdom the 

 function of furnishing the carbonic acid necessary to vegetation, and 

 chai-ging the plants with the office of ridding the atmosphere of this 

 impure gas and replacing it with oxygen. This notion, so specious 

 in appearance, but which has not been confiimed by experiment, 

 M. Martins endeavours to prevent his auditors from adopting. 

 Taking a general view of the vegetable kingdom, he observes, that 

 the green parts of plants are always the most numerous ; and that 

 during the night, plants vitiate the air instead of purifying it. But 

 in the winter season, we must observe, the action of plants on the 

 atmosphere almost entirely ceases, and, finally, in the day time and 

 in smnmer, the vivifying rays of the sun are frequently prevented by 

 clouds from reaching the earth. In conclusion, the Professor 

 observes, that the contrary action of the green and coloured parts of 

 plants balance each other, and thus the presence of vegetation 

 exercises, at most, but a very feeble influence on the composition of 

 the atmosphere. The experiments of Link, (Woodhouse, and 

 Grish, tend also to confirm this opinion. These experimenters 

 placed, under a large receiver, plants entirely covered with leaves, 

 flowers, and fruits ; after a considerable time the air of the receiver 

 was analysed, and its composition was found to be the same as before 

 the experiments : there was, in fact, a perfect equillibrium between 

 the different functions. What the air had gained in oxygen, by the 

 action of the green parts, was counterbalanced by the absorb- 

 tion of the coloured parts and their disengagement of carbonic acid ; 



