THE FARMERS' REGISTER. 



503 



ed thus serviceable to vegetation when they are 

 presented to the roots in a Huid stale ; and such is 

 the (act, that the compost of the I'arm-yard, the 

 crushed bones of the turnip cuHivator, the oil and 

 bones of fish, the <rypsum of the grazier, the 

 earths, lime, magnesia, and even silica, and all 

 the saline manures, are dissolved by son)e process 

 or other, belbre they can be absorbed by ve- 

 getables. 



SOURCE OF THE CARBON OF PLANTS. 



From Joiinston's Lectures. 



We have already seen reason to believe that 

 carbon is incapable of entering directly, in its solid 

 state, into the circulation of plants. It is sene- 

 rally considered, indeed, that solid substances of 

 every kind are unfit lor being taken up by the 

 organs of plants, and that only such as are in the 

 liquid or gaseous state, can be absorbed by the 

 minute vessels of which the cellular substances 

 of the roots end leaves of plants are composed. 

 Carbon, therefore, must enter either in the gaseous 

 or liquid Ibrm, but from what source must it be 

 derived 1 There are but two sources from which 

 it can be obtained, — the soil in which the plant 

 grows — and the air by which its stem and leaves 

 are surrounded. 



In the soil much vegetable matter is often pre- 

 sent, and the farmer adds vegetable manure in 

 large quantities with the view of providing food 

 for his intended crop. Are plants really fed by 

 the vegetable matter which exists in the soil, or 

 by the vegetable manure that is added to it 1 



This question has an important practical bear- 

 ing. Let us, therefore, submit it to a thorough 

 examination. 



We know, from sacred history, what reason 

 and science concur in confirmintr, that there was 

 a time when no vegetable matter existed in the 

 soil vyhich overspread the earth's surface. The 

 first plants must have grown without the aid of 

 either animal or vegetable matter — that is, they 

 must have been nourished from the air. 



It is known that certain marly soils, raised 

 from a great depth beneath the surlace, and con- 

 taining apparently no vegetable matter, will yet, 

 without manure, yield luxuriant crops, i'he 

 carbon in such cases must also have been derived 

 from the air. 



You know that some plants grow and increase 

 in size when suspended in the air, and without 

 being in contact with the soil. 



You know also, that many plants— bulbous 

 flower roots for example,— will grow and flourish 

 in pure water only, provided they are open to the 

 access ol" the atmospheric air. Seeds also will 

 germinate, and, when duly watered, will rise into 

 plants, though sown in substances that contain 

 no trace of vegetable matter. 



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 sitnilar circumstances Boussingault found 

 the seeds of trefoil increase in weight°2i times, 

 and wheat gave plants equal in weight, when dry, 

 to twice that of the original grains.* The 



Ann. de Chim. et de Phys. Ixvii. p. ]. 



] source of the carbon in all these cases cannot be 



doubted. 



When lands arc impoverished, you lay them 

 down to grass, and the longer they lie undisturbed 

 the richer in vegetable matter does the soil be- 

 come. When broke up, you find a black fertile 

 mould where little trace of organic matter had 

 previously existed. 



The same observation applies to lands lono- 

 under wood. The vegetable matter increases', 

 the soil improves, and when cleared and ploughed 

 it yields abundant crops of corn. 



Do grasses and trees derive their carbon from 

 the soil 7 Then how, by their growth, do they 

 increase the quantity of carbonaceous matter 

 which the soil contains 1 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 Ihey imparl to the soil. 



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 

 bosr, and finally a thick bed of peat is formed. 



Nor does this peat Ibrm and accumulate at the 

 expense of one species or genus of plants only,. 

 Latitude and local situation are the circumstances 

 which chiefly affect 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 

 Tierra del Fuego, "nearly every patch of level 

 ground is covered by two species of plants 

 lastdiapumila oi Brown, and donaiiamagellanica), 

 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 surliice of the islands, becomes 

 converted into this substance."* 



Whence have all these plants derived their 

 carbon? The quantity origmally contained in- 

 the soil is, after a lapse of years, increased tea 

 thousand fold. Has dead matter the power of re- 

 producing 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 aflbrding them, and as they died must 

 have left this carbon in a state unfit to nourish the 

 succeeding races. 



This reasoning appears unobjectionable, and, 

 from the entire group of facts, we seem justified 

 in concluding that plants every where, and under 

 all circumstances, derive the whole of their carbon 

 from the atmosphere. 



In certain extreme cases, as in those of plants 

 growing in the air and in soils perfectly void of 

 organic matter, this conclusion must be absolutely 

 true. The phenomena admit of no other inter- 

 pretation. But is it as strictly true of the more 

 usual forms of vegetable life, or in the ordinary 

 circumstances in which plants grow spontaneously 

 or are cultivated by the art of man ? Has the 



Darwin's Researches in Geology and Natural 

 History, pp. 349-50. Dr. Greville informs me that 

 the astelia approaches more nearly to the juncea or 

 rush tube, and the donatia to our tufted saxifrages 

 than to any other British plants. ' 



