270 Transactions. 



Aet. XXXII. — A Possible Relation between Atmospheric Carbon-dioxide and 



Leaf-development. 



By S. Page, B.Sc. 



[Bead before the Philosophical Institute of Canterbury, Ath August, 1909.] 



The existence of all green plants is dependent upon atmospheric carbon- 

 dioxide, and this is relatively so small in amount that the annual growth 

 of plants the world over absorbs each year a very appreciable proportion 

 of the whole supply. Liebig calculated that in Central Europe one acre 

 of vegetation removes three-fifths of a ton of carbon per year ; and 

 Arrhenius,* using this estimate, finds the annual carbon - production of 

 plants the world over to be 13,000 million tons — not less than one-fiftieth 

 of the whole CO 2 of the atmosphere. Although the greater part of this, 

 by decay, goes back into the air each year, Arrhenius estimates that the 

 carbon annually obtained from the air and stored up as peat would use up 

 all the atmospheric CO 2 in ten thousand years. 



Existing peat and fossil carbon generally, corresponds approximately in 

 amount to the oxygen of the air — that is, would require the whole of the 

 atmospheric oxygen to burn it up completely. Hence it was suggested by 

 Keohne, of Brussels, in 1856, that all the oxygen of the air — 1,216 billion 

 tons — may have been produced from CO 2 by plants. 



It is clear, then, that the relation between plants and the world's supply 

 of CO 2 is a very intimate one, and that any considerable fluctuations in the 

 aerial proportion of this essential gas is hkely to be of supreme importance 

 to plant hfe. That fluctuations have occurred — that at one time in the 

 earth's history the amount of CO 2 in the atmosphere was very different 

 from and very much greater than at present— there is a good deal of evi- 

 dence to show. There can be no doubt that at one time the crust of the 

 earth was at a high temperature, above its melting-point, and far above 

 the ignition-point of carbon in air. Hence any free carbon whatever which 

 reached the surface of the fluid earth during this period — a very long period 

 — must have been burnt into CO2. Not only so, but the free carbon 

 below the surface, protected from air, could scarcely escape oxidation by 

 the water and metallic oxides of the molten mass. 



Practically all metallic oxides are now known to be reducible by carbon at 

 very high temperatures, and many igneous rocks, old and new, undoubtedly 

 contained considerable water while in fluid or semi-fluid condition. 



It has been suggested by Mendeleef and others that at this stage the 

 carbon escaped oxidation by forming metalhc carbides similar to the iron- 

 carbides of cast iron and the now well-known calcium-carbide used for 

 generating acetylene. But carbides are readily oxidized into CO 2 by 

 water, air, or metallic oxides. Examples of such action are found in the 

 Bessemer converter and in the production of steel from^ cast iron by burning 

 out the contained carbon with oxides of iron. The traces of CO 2 now found 

 occasionally in rocks in the Hquid form may possibly have their origin in 

 some such deep-seated oxidation of carbon or carbides. 



The weight of evidence, then, appears against the supposition that the 

 bulk of the earth's carbon was retained in the' crust dming the hot period, 



H: (' 



Worlds in the Making." 



