ORGANIC CHEMICAL PROCESSES. 



27 



by the same influence : a soil receives mor. 

 carbon in this form than its decaying humus 

 had lost as carbonic acid. 



Plants do not exhaust the carbon of a soi 

 in the normal condition of their growth; on 

 the contrary, they add to its quantity. Bu 

 if it is true that plants give back more car- 

 bon to a soil than they take from it, it is evi- 

 dent that their growth must depend upon the 

 reception of nourishment from the atmo- 

 sphere in the form of carbonic acid. The 

 influence of humus upon vegetation is ex- 

 plained by the foregoing facts in the most 

 clear and satisfactory manner. 



Humus does not nourish plants by bein 

 taken up and assimilated in its unaltere 

 state, but by presenting a slow and lasting 

 source of carbonic acid, which is absorbed 

 by the roots, and is the principal nutriment 

 of young plants at a time when, being des- 

 titute of leaves, they are unable to extract 

 food from the atmosphere. 



In former periods of the earth's history, 

 its surface was covered with plants, the re- 

 mains of which are still found in the coal 

 formations. These plants the gigantic 

 monocotyledons, ferns, palms, and reeds 

 Velong to a class to which nature has given 

 tne power, by means of an immense exten- 

 sion of their leaves, to dispense with nour- 

 ishment from the soil. They resemble in 

 this respect the plants which we raise from 

 bulbs and tubers, and which live while 

 young upon the substances contained in 

 their seed, and require no food from the soil 

 when their exterior organs of nutrition are 

 formed. This class of plants is even at 

 present ranked amongst those which do not 

 exhaust the soil. 



The necessity of the existence of plants 

 such as these at the commencement of ve- 

 getation, must now be apparent. Humus 

 is a product of the decay of vegetable mat- 

 ter, and therefore could not have existed 

 to supply the first plants with the food neces- 

 sary for the development of the more deli- 

 cate kinds. Hence the plants capable of 

 flourishing under such circumstances could 

 only be those which receive their nourish- 

 ment from tne air alone. By their decay, 

 however, the soil in which they grew be- 

 came supplied with vegetable matter, and 

 the progress of vegetation must have fur- 

 nished to the earth materials adapted for the 

 development of those plants, which depend 

 upon the nutriment contained in the soil, 

 until those organs are formed which are des- 

 tined for the assumption of nourishment 

 from the atmosphere. 



The plants of every former period are dis- 

 tinguished from those of the present by the 

 inconsiderable development of their roots. 

 Fruit, leaves, seeds, nearly every part of the 

 plants of a former world, except the roots, 

 are found in the brown coal formation. The 

 vascular bundles, and the perishable cellular 

 tissue, of which their roots consisted, have 

 been the first to suffer decomposition. But 

 when we examine oaks and other trees, 



which in consequence of revolutions of the 

 same kind occurring in later ages have un- 

 dergone the same changes, we never find 

 their roots absent. 



The verdant plants of warm climates are 

 very often such as obtain from the soil only 

 a point of attachment, and are not dependent 

 on it for their growth. How extreme!? 

 small are the roots of the Cactus, Sedum> 

 and Sempervivum, in proportion to their 

 mass, and to the surface of their leaves! 

 Large forests are often found growing in 

 soils absolutely destitute of carbonaceous 

 matter; and the extensive prairies of the 

 western continent show that the carbon 

 necessary for the sustenance of a plant may 

 be entirely extracted from the atmosphere. 

 Again, in the most dry and barren sand, 

 where it is impossible for nourishment to be 

 obtained through the roots, we see the milky- 

 juiced plants attain complete perfection. 

 The moisture necessary for the nutrition of 

 these plants is derived from the atmosphere, 

 and when assimilated is secured from eva- 

 poration by the nature of the juice itself. 

 Caoutchouc and wax, which are formed in 

 these plants, surround the water, as in oily 

 emulsions, with an impenetrable envelope 

 by which the fluid is retained, in the same 

 manner as milk is prevented from evaporat- 

 ing by the skin which forms upon it. 

 These plants, therefore, become turgid with 

 their juices. 



Particular examples might be cited of 

 plants, which have been brought to maturity, 

 upon a small scale, without the assistance 

 of mould ; but fresh proofs of the accuracy 

 of our theory respecting the origin of carbon 

 would be superfluous and useless, and 

 could not render more striking, or more con- 

 vincing, the arguments already adduced. It 

 must not, however, be left unmentioned, 

 that common wood charcoal, by virtue 

 merely of its ordinary well-known proper- 

 ties, can completely replace vegetable mould 

 or humus. The experiments of Lukas, 

 which are appended to this work, spare me 

 all further remarks upon its efficacy. 



Plants thrive in powdered charcoal, and 

 may be brought to blossom and bear fruit if 

 exposed to the influence of the rain and the 

 atmosphere; the charcoal may be previously 

 heated to redness. Charcoal is the most 

 indifferent" and most unchangeable sub- 

 stance known ; it may be kept for centuries 

 without change, and is, therefore, not sub- 

 ject to decomposition. The only substances 

 which it can yield to plants are some salts, 

 which it contains, amongst which is silicate 

 of potash. It is known, however, to pos- 

 sess the power of condensing gases within 

 its pores, and particularly carbonic acid. 

 And it is by virtue of this power that the 

 roots of plants are supplied in charcoal, ex- 

 actly as in humus, with an atmosphere of 

 carbonic acid and air, which is renewed as 

 quickly as it is abstracted. 



In charcoal powder, which had been used 

 for this purpose by Lukas for several years. 



