178 
GARDENING AS A SCIENCE. 
chemical accuracy ; but they by no means elucidate causes. In order, thereforej 
to obtain a glimpse of these, we ought to consider the law of electric inductioDj 
which teaches that whenever any electrized body approaches another body, it 
induces or excites an opposite, or different electric condition therein ; and that 
these conditions produce mutual attraction. Oxygen and hydrogen gases are thus 
ill different electric conditions, and they are disposed to unite together suddenly 
and with violence, or progressively and without explosion ; in either case watery 
vapour is the product. This undoubted fact leads to the inference that oxygen 
and liydrogen are vehicles of two distinct electricities, or that they are themselves 
electrics^ ever tending to unite, and producing by their union multifarious pheno- 
mena which we term meteorological. 
Carhon (vulgo, charcoal) is found in the woody fibre of vegetables — and as 
a residuum of the combustion of vegetable substances. According to Liebig, an 
atmosphere of carbonic acid pervades the soil wherein humus, or decaying vege- 
table matter is present. 
Carbonic acid is produced by the union of carbon vapour and oxygen gas ; it 
is the result either of active or slow combustion, and is a product of electro- 
cliemical attraction. 
Nitrogen exists in the atmosphere ; it is also a component of ammonia, of 
nitrous acid, and of most animal, and many vegetable, bodies. 
We thus liave before our eyes the chief elements of all the plants with which 
we are acquainted — other substances, as salts, alkalies, and earths, are traceable in 
the ashes of plants, and occasionally in their juices ; but these being derivable from 
the earth in a state of watery solution, and varying according to local circumstances, 
we may set aside, as not affecting the present inquiry. 
Assuming, then, the hypothesis (which, till positively refuted, we consider as 
more than probable) that every chemical phenomenon in nature, every act of union 
and decomposition, is induced by the electrising agency of the sun, we obtain 
four agents, which we term elements, that are ever present in the air, water, and 
earth ; and ready to combine under the influence of electricity, as exerted by the 
vegetable vital principle. 
Connecting these facts with the structure of the organism (Liebig's expressive 
word), we perceive that each instrument, eaeli portion of the mechanism, is 
perfect. We find in the roots and stems a variety of tissues, vascular and cellular, 
appropriate to the absorption and deposition of the fluids derived from the soil ; 
and, in the structure of the foliage, tissues similar in character, connected with 
orifices, or oscular pores, (stomaia,) by and through which, the gases of the 
atmosphere, and those developed in the plant, can pass interchangeably ; and, 
finally, by the analysis of all the products, we are enabled to conjecture that the 
elements of all these products are derived from the earth and air. 
It is an axiom in philosophy, that nothing ever can be lost, or extinguished. 
A change of form and condition is for ever in progress; plants derive their 
