GARDENING AS A SCIENCE. 
179 
quite at variance with the laws of growth and development. A spirit of research 
is estimable, and may lead to discoveries ; but what conclusion in any degree 
satisfactory can be attained, when the means are opposed to the principles of 
nature ? 
Thus it happened some years ago, when physiologists endeavoured to discover 
the conducting vessels of the sap by the immersion of juicy cuttings of trees and 
shrubs into coloured infusions : the colouring matter passed into the cellular 
system, ascended, and was traced into the leaves. But the cuttings were mutila- 
tions^ and thus afforded no correct natural evidence. That great philosopher, 
Mr. Knight, felt the truth of the objection, and a few years before his decease, 
alluding to an experiment by Amici, which had excited much interest, wrote thus 
upon what he styled " the folly and extravagance of the inferences drawn there- 
from : — " A small detached part of a plant growing naturally under water " (Chara) 
"is so placed, that one of its sides is subjected to the action of intense light, and 
probably, considerable heat, if solar light be used ; and the fluids are seen to rise 
on the illuminated side, and descend on the other. A part of the body of a leech 
subjected to the same treatment, would have afforded nearly as good evidence 
respecting the motions of the blood in the human hody." 
"While it remains an undoubted fact that dark fluids will ascend through 
mutilated channels, and produce defined dots and streaks in parts far remote from 
their lower extremities, it is equally certain that in plants of tissue so lax and juicy 
as that of the balsam^ not a particle of colour can be introduced by the roots, however 
long they may be watered with coloured infusions. Hence, we conclude that by the 
application of unnatural machinery and agents, no correct natural results can ever 
be attained. 
But by whatever aliment a deep and healthy tint of foliage is produced, 
there is reason to conclude that to a greater or less extent the flowers or fructiferous 
system will be improved ; and as vegetable matter is proved in many instances to 
confer intensity of colour, it becomes the duty of the philosophic inquirer to 
investigate minutely and note down the effects of various composts. And hereupon 
we would observe that, as a general fact, masses of semi-decayed leaves are most 
favourable to culinary vegetables and melons ; whereas for pot culture, the earth of 
leaves or vegetable mould, obtained by the operation of the w^eather, and occasional 
turning over during three years, is required. 
As respects quality, the leaves of oak and beech, beaten off the trees in autumn, 
while yet green, produce the best heating material ; but in ornamental gardening, 
the preference appears due to the mould obtained from the soft- leaved trees and 
shrubs, which ferment and decompose rapidly. Most persons would object to 
those of evergreens, especially the common laurel ; though it has been observed 
that the leaves of the fir tribe yield an earth more closely resembling that of heath 
soil than those of any other trees. 
American plants, as they are styled, prosper abundantly by being dressed every 
