CHEMISTRY OF HORTICULTURE. 
229 
It is a greenhouse species, flowering profusely from July to the end of the season. 
The ordinary management of perennial Begonias is sufficient to ensure a good bloom 
with this species. 
Our drawing was made from a specimen which flowered in the stove of Messrs. 
Henderson's in October, 1848. 
Propagation is effected by cuttings and seeds. 
The name Begonia is given in honour of Michael Begon, a botanist of the seventeenth 
century. 
CHEMISTRY OF HORTICULTURE. 
By John Totoers, Esq. 
(Continued from Page 198.) 
Atmospheric Phenomena claim notice as they are multiform and of deep interest. In 
the last article the two essential constituents of atmospheric air, which always combine in 
definite proportions, were treated of as constant elements; while two others, which are found 
in its volume, namely watery vapour and carbonic acid, are classed as variable elements. 
But there is a third which must not be passed over in silence, as it is always present, though 
to what extent, philosophy does not appear able to determine, — this is Ammonia, that com- 
bination of two of the gases, hydrogen and nitrogen, which was mentioned at page 166, and 
also at page 203 of the " Magazine of Gardening and Botany." Liebig was the first chemist 
who, in the first edition of his work on Agricultural Chemistry, attached importance to the 
ammonia that assuredly exists in the atmosphere ; but modern theory, taken up by ardent 
young persons, went too far when it assumed that " plants obtain all their nitrogen from 
the ammonia which floats in the atmosphere." If, however, we recollect that there is not 
a decaying substance containing nitrogen, scattered over the earth's surface, that does not 
evolve some ammonia, it will be difficult to entertain a doubt of its actual presence in the 
atmospheric air ; and in fact, direct experiments upon snow and the purest rain water 
have determined its existence therein. The smoke from coals contains also a volume of 
ammoniacal salts; and it would not be unsafe to conjecture that, by the energy of electricity, 
the nitrogen of the air, and the hydrogen of its watery vapour, are induced to combine in the 
exact proportions which form ammoniacal gas. Under whatever circumstances or propor- 
tions ammonia may actually exist, certain it is that every shower will convey some of it to 
the surface of the earth, and thus, through the wise economy of nature, give fertility to the 
numerous varieties of farm and garden plants, which demand the product of decay and 
putrefaction. How wonderful and admirable are those ceaseless changes which result from 
the grand law that nothing ever was, nor should be, lost ! ! 
One additional remark upon the composition of the atmosphere may be hazarded ; it is 
generally asserted that, " the essential gases oxygen and hydrogen exist in a state of merely 
mechanical mixture, and by no means, as some have supposed, in chemical combination." 
It would be difficult to set aside this rather modern hypothesis, especially since some of 
the most striking experiments tend to establish it. For instance, the formation of nitrous 
acid is induced by passing a succession of electric sparks through a small volume of pure 
atmospheric air contained in a glass tube : on the other hand, it appears unphilosophical to 
suppose that two gases so undeviatingly constant, so unvarying in proportion and quality, 
- — be their situation throughout the world what it may — could exist in a state of mere 
mechanical mixture ! Such a mixture implies an interfiltration only, an intersticial position 
of particles, under the law of Dalton, that " each and every gas becomes a vacuum to 
other gases; " whereas, that permanent and uniform blending of the two atmospheric gases, 
which has existed without alteration since the commencement of time, seems to require the 
presence of an agent which should convert the two constituents into one perfect and homo- 
geneous medium, exactly suitable to the requirements of every being that inspires the 
