68 NUTRITION IN VEGETABLES. 
pounded carbon, none of it will be taken up, for after several 
months, the whole of the carbon will still be found in the ves- 
sel. The spongioles cannot continue long to absorb a thick 
or viscid fluid, as they would be clogged up by it, and hence 
a plentiful supply of water is necessary. Water also affords 
two of the most necessary elements of vegetable matter, Oxy- 
gen and hydrogen; and when there is a deficiency of de- 
cayed organic matter, the water derived from the atmosphere _ 
must be the principal source from which these elements are 
procured. It is probably chiefly in the form of carbonic 4 
that carbon enters the roots of plants. This compound’ 
formed abundantly during the decomposition of organic 
dies, and is absorbed in large proportion by water. Muci- 
lage and sugar also contain oa quantities of carbon, in 
soluble state. 
239. Four kinds of earth are generally found in soils: alu- 
mina, argil, or clay ; sand or silex; lime or calcareous earth 
and magnesia, These constitute two principal kinds 
soils ; stiff, from an excess of clay, or what is called 
laceous ; or dry, loose, and sandy, from an excess of siliceous 
. 
“ The silica in soils is usually combined with alumina 
: ee alumina, lime, magnesia, and oxide 
of iron, forming gravel and sand of different degrees of fine- 
ness. The carbonate of lime is usually in an impalpable form, 
but sometimes in the state of caleareous sand. ‘The magne 
sia, if not combined with the gravel and sand of soil, is ina 
fine powder united to carbonic acid, The impalpable part of 
the soil, which is usually called clay or loam, consists of sili- 
ea, alumina, lime and magnesia.”—‘‘ The vegetable and ani- 
mal matters are sometimes fibrous, sometimes entirely bro- 
ken down and mixed with the soil.”—Davy’s 
