1849.] On the Influence of Forests on Climate. 795 



Chili on their western declivities, but none falls on the plains to the 

 eastward except occasionally, when the wind blows from the Atlantic." 



Again, Dr. Daubeny has ascertained by experiments communicated 

 to the British Association, that plants undoubtedly exercise a purifying 

 influence on the atmosphere. In a letter to Dr. John Lindley, he 

 expresses himself thus :*-<— 



" As the observations of Ellis left it in some doubt whether the 

 balance was in favour of the purifying or the deteriorating influence 

 upon the air which is exercised by plants during different portions of 

 the day and night, I conducted my experiments in such a manner that 

 a plant might be inclosed in a jar for several successive days and nights, 

 whilst the quality of the air was examined at least two or three times 

 a day, and fresh carbonic acid admitted as required. A register being 

 kept of the proportion of oxygen each time the air was examined, as 

 well as of the quantity of carbonic acid introduced, it was invariably 

 found that, so long as the plant continued healthy, the oxygen went 

 on increasing, the diminution by night being more than counter- 

 balanced by the gain during the day. This continued until signs of 

 unhealthiness appeared in the confined plant, when of course the oxygen 

 began to decrease." 



" In a perfectly healthy and natural state, it is probable that the 

 purifying influence of a plant is much greater, for when I introduced 

 successively different plants into the same air, at intervals of only a few 

 hours, the amount of oxygen was much more rapidly increased, in one 

 instance to more than 40 per cent, of the whole, instead of twenty as 

 in the air we breathe." 



" Thus the vegetable kingdom may be considered as a special pro- 

 vision of nature to consume that which would render the world unin- 

 habitable by man, and to have been so beautifully contrived that its 

 existence depends upon its perpetual abstraction of that, without the 

 removal of which our own existence could not be maintained. But 

 although this is true of green plants, it does not appear to be so, of 

 Fungi. Marcet has shewn from carefully conducted experiments, that 

 Mushrooms, vegetating in atmospheric air, produce on that air very 

 different modifications from those of green plants in analogous situ- 

 ations, in fact, that they vitiate the air promptly, either by absorbing 



* Vide Lindley's Introduction to Botany, p. 378, 3rd Edition. 



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