10 
GARDENING AS A SCIENCE. 
Camellias^ on tlie contrary, and vast numbers of tlie hard- wooded species, affect 
a sliady situation ; in which the rich verdure of their foliage is better sustained. 
It may therefore be laid down as an axiom established by facts, that they who 
endeavour to attain perfection of growth in a miscellaneous collection of plants, 
whose habits are dissimilar, must compound for disappointment. We talk of 
climate, country, and natural habits, and propose to study them as tutors. The 
curious in botanical and physiological rescarcli do well to indulge in these inquiries ; 
but they arc not essential to the practical English gardener. To him experience 
and observation of results will afford the surest guides on which to found a theory ; 
for, as every imported exotic is at once placed in a situation, which in no respect 
corresponds with that from which it was removed, its future prosperity must 
depend upon artificial appliances. Temperature is a secondary consideration ; 
since it has been proved that the variable nature of the British climate destroys 
many plants which sustain without injury the rigours of a Siberian winter. But 
light and its modifications are essential : for not a ray passes through the medium 
of the most transparent crown-glass, that does not suffer some degree of what is 
called decomposition. Every ray also is more or less bent, and its heating and illumi- 
nating powers reduced, as may be proved by the following very simple experiment. 
If a spare light be rested against a south garden wall, so that it form a sharp slope, 
and two correct thermometers be suspended against the wall, one under the centre 
of the light, and the other exterior of it, the latter at mid-day, exposed to the 
utmost fervour of the sun, will indicate a heat much greater than the one under 
the glass, to the extent sometimes of 10 to 12 degrees. We learn more than one 
truth by this investigation. Glass interrupts the power of the sun ; the air, in 
either situation, having little to do in regulating temperature. The comparative 
differences vary extremely in their degrees, proving that the power of the solar ray 
is not dependent upon greater or less brilliancy ; and again, the glass, though it 
defend the plants, decidedly abates temperature ; and, therefore, they reason 
erroneously who ascribe the heat of forcing-houses, and the maturation of plants, 
to the heating medium of the glass. Glass abounds with globules, which act as so 
many lenses, and produce burning points; it also diffuses a moderated illumination; 
but the main advantages are derived from its retention of an equable temperature, 
and the opportunity afforded to govern the due admission of external air. And 
these considerations instruct us to study the availability of air by the sliding sashes. 
We drop this hint in order to induce reflection, but to pursue the inquiry now 
would be remote from our present subject. 
Light, in its nature, cannot be understood or defined ; it assuredly is an 
emanation from the sun ; but this is a bald truism : that it induces stupendous, 
electro-magnetic phenomena, by acting on and under the surface of the earth, is 
equally certain ; and thus, by an induced voltaic action upon water and metallic 
substances, heat, magnetism, and meteorological electricity are developed. We 
may safely insist upon these general deductions while deprecating a dogmatic 
