WHENCE PLANTS DERIVE THEIR CARBON. 59 



Thus De Saussure found that two beans, when caused to vegetate in 

 the open air on pounded flints, doubled the weight of the carbon they 

 originally contained. 



Under similar circumstances Boussingault found the seeds of trefoil 

 increased in weight 2i times, and wheat gave plants equal in weight, 

 when dry, to twice that of the original grains, [Ann. de Chim. etde Phys. 

 Ixvii., p. 1.] The source of the carbon in all these cases cannot be 

 doubted. 



4°. When lands 4ire impoverished, you lay them down to grass, and 

 the longer they lie undisturbed the richer in vegetable matter does the 

 soil become. When broken up, you find a black fertile mould where 

 little trace of organic matter had previously existed. 



The same observation applies to lands long under wood. The vege- 

 table matter increases, the soil improves, and when cleared and plough- 

 ed it yields abundant crops of corn. 



Do grasses and trees derive their carbon from the soil ? Then, how, 

 by their growth, do they increase the quantity of carbonaceous matter 

 which the soil contains ? It is obvious that, taken as a whole, they 

 must draw from the air not only as much as is contained in their own 

 substance, but an excess also, which they impart to the soil. 



5°. But on this point the rapid growth of peat may be considered as 

 absolutely conclusive. A tree falls across a little running stream, dams 

 up the water, and produces a marshy spot. Rushes and reeds spring 

 up, mosses take root and grow. Year after year new shoots are sent 

 forth, and the old plants die. Vegetable matter accumulates ; a bog, 

 and finally a thick bed of peat is formed. 



Nor does this peat form and accumulate at the expense of one spe- 

 cies or genus of plants only. Latitude and local situation are the cir- 

 cumstances which chiefly effect this accumulation of vegetable matter 

 on the soil. In our own country, the lowest layers of peat are formed 

 of aquatic plants, the next of mosses, and the highest of heath. In 

 Terra del Fuego, " nearly every patch of level ground is covered by 

 two species of plants (fl^feZm pwmzZa of Brown, and donatia magellan- 

 ica)t which, by their joint decay, compose a thick bed of elastic peat." 

 " In the Falkland Islands, almost every kind of plant, even the coarse 

 grass which covers the whole surface of the island, becomes converted 

 into this substance."* 



Whence have all these plants derived their carbon ? The quantity 

 originally contained in the soil is, after a lapse of years, increased ten 

 thousand fold. Has dead matter the power of reproducing itself? 

 You will answer at once, that all these plants must have grown at the 

 expense of the air, must have lived on the carbon it was capable of af- 

 fording them, and as they died must have left this carbon in a state un 

 fit to nourish the succeediilg races. 



This reasoning appears unobjectionable, and, from the entire group of 

 %cts, we seem justified in concluding that plants every where, ajid 

 under all circumstances, derive the whole of their carbon from the at- 

 mosphere. 



' Darwin's Researches in Geology and Natural History^ pp. 349-50. Dr. Gerville informs 

 me that the astelia approaches more nearly te the junceae or rush tribe^ and the donalia to our 

 tufted saxifrages, than to any other British ciiits. 



