THE ART OF CULTURE. 



43 



sufficient to supply the whole of the present 

 generation of living beings with carbon for 

 a thousand years, even if it were not re- 

 newed. Sea-water contains j^^^-y of its 

 weight of carbonate of lime; and this quan- 

 tity, although scarcely appreciable in a 

 pound, is the source from which myriads 

 of marine mollusca and corals are supplied 

 with materials for their habitations. 



Whilst the air contains only from 4 to 6 

 ten-thousandth parts of its volume of car- 

 bonic acid, sea-water contains 100 times 

 more, (10,000 volumes of sea- water contain 

 620 volumes of carbonic acid Laurent, 

 Bouillon, Lagrange.) Ammonia* is also 

 found in this water, so that the same condi- 

 tions which sustain living beings on the land 

 are combined in this medium, in which a 

 whole world of other plants and animals 

 exist. 



The roots of plants are constantly en- 

 gaged in collecting from the rain those 

 alkalies which formed part of the sea- water, 

 and also thoj;e of the water of springs, 

 which penetrates the soil. Without alkalies 

 and alkaline bases most plants could not 

 exist, and without plants the alkalies would 

 disappear gradually from the surface of the 

 earth. 



When it is considered, that sea-water con- 

 taius less than one-millionth of its own 

 weight of iodine, and that aU combinations 

 of iodine with the metallic bases of alkalies 

 are highly soluble in water, some provision 

 must necessarily be supposed to exist in the 

 organization of sea-weed and the different 

 kinds of Fuci, by which they are enabled 

 'luring their life to extract iodine in the 

 form of a x soluble salt from sea-water, and 

 to assimilate it in such a manner, that it is 

 not again restored to the surrounding me- 

 dium. These plants are collectors of iodine, 

 just as land plants are of alkalies ; and they 

 yield us this element, in quantities such as 

 we could not otherwise obtain from the 

 water without the evaporation of whole 

 seas. 



We take it for granted that the sea-plants 

 require metallic iodides for their growth, and 

 that their existence is dependent on the 

 presence of those substances. With equal 

 justice, then, we conclude, that the alkalies 

 and alkaline earths, always found in the 

 ashes of land-plants, are likewise necessary 

 for their developement. 



CHAPTER VII. 



THE ART OF CULTURE. 



THE conditions necessary for the life of 

 all vegetables have been considered in the 



* When the solid saline residue obtained by the 

 evaporation, of sea-water is heated in a retort to 

 redness, a sublimate of sal-ammoniac is obtained. 

 -MAKCET. 



preceding part of the work. Carbonic acid, 

 ammonia, and water yield elements for all 

 the organs of plants. Certain inorganic 

 substances salts and metallic oxides serve 

 peculiar functions in their organism, ano 

 many of them must be viewed as essential 

 constituents of particular parts. 



The atmosphere and the soil offer the same 

 kind of nourishment to the leaves and roots. 

 The former contains a comparatively inex- 

 haustible supply of carbonic acid and am- 

 monia ; the latter, by means of its humus, 

 generates constantly fresh carbonic acid, 

 whilst, during the winter, rain and snow in- 

 troduce into the soil a quantity of ammonia, 

 sufficient for the developement of the leaves 

 and blossoms. 



The complete, or it may be said, the abso- 

 lute insolubility in cold water of vegetable 

 matter in progress of decay, (humus,) ap- 

 pears on closer consideration to be a most 

 wise arrangement of nature. For if humus 

 possessed even a smaller degree of solubility 

 than that ascribed to the substance called hu- 

 mic acid, it must be dissolved by rain-water. 

 Thus, the yearly irrigation of meadows, 

 which last for several weeks, would remove 

 a great part of it from the ground, and a 

 heavy and continued rain would impoverish 

 the soil. But it is soluble only when com- 

 bined with oxygen ; it can be taken up by 

 water, therefore, only as carbonic acid. 



When kept in a dry place, humus may be 

 preserved for centuries; but when moist- 

 ened with water, it converts the surrounding 

 oxygen into carbonic acid. As soon as the 

 action of the air ceases, that is, as soon as it is 

 deprived of oxygen, the humus suffers no far- 

 ther change. Its decay proceeds only when 

 plants grow in the soil containing it ; for 

 they absorb by their roots the carbonic acid 

 as it is formed. The soil receives again from 

 living plants the carbonaceous matter it thus 

 loses, so that the proportion of humus in it 

 does not decrease. 



The stalactitic caverns in Franconia, and 

 those in the vicinity of Baireuth, and Streit- 

 berg, lie beneath a fertile arable soil; the 

 abundant decaying vegetables or humus in 

 this soil, being acted on by moisture and air, 

 constantly evolve carbonic acid, which is dis- 

 solved by the rain. The rain-water thus 

 impregnated permeates the porous lime- 

 stone, which forms the walls and roofs of 

 the caverns, and dissolves in its passage as 

 much carbonate of lime as corresponds to 

 the quantity of carbonic acid contained in it. 

 Water and the excess of carbonic acid eva- 

 porate from this solution when it has reached 

 the interior of the caverns, and the limestone 

 is deposited on the walls and roofs in crys- 

 talline crusts of various forms. There are 

 few spots on the earth where so many cir- 

 cumstances favourable to the production of 

 humate of lime are combined, if the hurnua 

 actually existed in the soil in the form of 

 humic acid. Decaying vegetable matter, 

 water, and lime in solution, "are brought to- 

 gether, but the stalactites formed contain no 



