428 Development of Roots of Agricultural Plants. 
no evidence to show that they are capable of generating bodies 
which at present defy the power of analysis. If potassium, sodium, 
calcium, and other elementary bodies, therefore, exist in plants 
in greater quantities than could be contained in a bulk of the sur- 
rounding fluid equal to that which traverses the tissue in a given 
time, these must have some especial power of abstracting it from 
without. One of the most curious instances on record is that 
afforded by the ash contents of certain parasites, as misletoe, com- 
pared with those of the plants on Avhich they grow, though they 
draw their nourishment from sap already partially elaborated. 
Where the quantity is less than might be expected, it becomes 
a question whether roots have not some power of getting rid of 
superfluous matter, a subject which we shall come to presently. 
It is well known that soils have great power of absorbing into 
their substance, or, at least, of attracting, different matters Avhich 
pass through them, as nitrogen by clay, and that in so stable a 
form that water passing through the mass, even when strongly im- 
pregnated with carbonic acid, will not extract them, though under 
certain conditions the various salts are slowly soluble, Schleiden 
some years since endeavoured to show that the only use of vege- 
table soil was to serve as a storehouse for nutritive matters, — an 
extreme view which will not very readily meet with general 
acceptance. Some authors regard the spongelets as acting by 
mere mechanical or chemical rules, without allowing any especial 
power to them as endowed with life. According to this view, 
matters enter them precisely in the same manner as if the walls 
of the component cells consisted of mere dead membranes, and 
their contents were a mere chemical solution. It is clear, however, 
that something far removed from any form of capillarity must be 
at work, and though something may be attributed to the different 
rates of penetration of different substances when mixed together, 
and not in chemical combination, it seems impossible to deny the 
existence of some higher power, which, for the want of anything 
more definite, may well pass under the name of vital energy, or 
vitality. Without attaching any mysterious notion to the term 
life, Ave cannot be wrong in using it merely as an expression for 
those phenomena which take place in living organisms, but which 
would never take place in mere mechanical apparatus, and which 
cannot be imitated by artificial methods at present known. I say 
at present known, because it is impossible to predict what may 
be effected by modern chemistry. One step at least has been 
made in the production of a substance like alcohol from inorganic 
materials, hitherto supposed to require organic matter for its 
formation. 
It is, however, time to consider the excrementitious powers of 
roots ; for if they have the means of getting rid of any excess of 
