392 Mr. E. H. Cook on Carbon Dioxide 



Thus the land-surface bearing vegetation capable of decom- 

 posing carbon dioxide amounts to 49,400,000 square miles. A 

 large portion of this land, however, is uncovered by vegeta- 

 tion : cities are built on it; barren mountains rise out of it; 

 and large rivers run through it. Estimating the absolute 

 area of leaf (i. e. chlorophyll-bearing organs) borne by the 

 plant-bearing land of the earth as 50 per cent, of the total 

 area, we find that 24,700,000 square miles of leaf are en- 

 gaged in purifying the atmosphere. This is equal to about 

 63,973,000,000,000 square metres, which gives the number of 

 litres of C0 2 decomposed per hour. But sunlight only lasts, 

 on an average, about ten hours a day; consequently the total 

 amount daily decomposed is equal to ten times this amount. 

 Finally, allowing 25 per cent, for the diminution of the action 

 which takes place in winter, we find that the enormous amount 

 of 479,000 millions of kilolitres, or over 900,000 millions of 

 kilogrammes of carbon dioxide are decomposed daily. This 

 amount is much greater than that produced from all sources 

 taken together. But it must be remembered that a large por- 

 tion of the carbon thus withdrawn by plants during the spring 

 and summer months is returned to the air again by the decom- 

 position of the leaf in autumn. Although we have allowed for 

 this above, yet if plant-action is anything like so powerful as 

 these calculations show, that allowance will have to be consi- 

 derably increased. Again, a reduction, and perhaps a consi- 

 derable one, will have to be made on account of the respiration 

 which has been proved to take place in some plants during 

 the hours of darkness; but I am unable to find an account of 

 any experiments upon this point. The magnitude of this 

 action given by these calculations is astonishing. This paper 

 was commenced under the idea that the action usually attri- 

 buted to plants was greatly overestimated, and that their 

 purifying effect was exaggerated. It will be seen that the 

 vegetable life on the globe is sufficient of itself to keep up 

 the purity of the air. The author wishes this statement to be 

 received with caution, because of the unsatisfactory nature 

 of the fundamental experiment upon which the calculations 

 are based, and also of our total want of knowledge of the 

 amount of plant-respiration. This latter action may be much 

 greater than is usually supposed. 



The second great action going on in nature is effected by 

 the interposition of animal life. It consists in the removal 

 from sea-water of the carbon dioxide held by it in solution by 

 certain low forms of animal life. The most important of these 

 are Actinozoa and Foraminifera — the former being concerned 

 in the building of coral reefs, and the latter in forming those 



