REVIEW. 
131 
spent, so as to reduce the heat of the fermenting substance to almost nothing, 
then, and not until then, is it in a fit state to receive the plants into it. That 
there are in practice means used to prevent these evils I admit, but so far are 
they from being perfect, they only serve to prove that the greatest degree of heat 
is exactly where least of it is required; as for instance, the well known practice 
of placing a slate under each hill of earth where the plants are planted, for the 
purpose of keeping down the steam, and of pouring cold water under them to 
kill the excessive heat in that part of the bed, demonstrates, not only that most 
heat exists, where least of it is required, but also, that a great deal of it is, con 
trary to what it ought to be, wasted or destroyed. 
Another great evil is, the bed being composed entirely of fermenting sub¬ 
stances ; it settles so much as to render it almost impossible, after the heat has 
once abated, to renew the same by the assistance of fresh linings when it is 
required. To obviate this evil, T. A. Knight, Esq. P. H. S. has recommended 
the “placing a thin iron or wood n tube from front to back of the leaves or 
dung composing the bed, and at about one third of its height from the top. 
This tube is one inch and a half in diameter, opens at both ends, but is intended 
to be opened or closed by plugs at pleasure. Threesmaller tubes of three quarters 
of an inch in diameter, are inserted at equal distances into the large one, which 
rise through the dung and mould of the bed, and discharge by lateral holes near 
their tops the heated air which rises from the large tube.” 
Further, some persons have recommended the use of platforms, on which are 
placed the frame, earth, and the, whole are supported by posts or brick piers. 
The space beneath the floor is filled with hot dung, and in some cases, a lining 
is applied round the outside. The author had a structure of this kind under his 
charge for several years, and although the best cucumbers which ever came un¬ 
der his notice were produced in it, and Balsams sixteen feet in circumference, 
yet for want of a proper substance against which to build the linings, and the 
almost entire destitution of means to supply heat by absorbtion and conduction, 
experience has taught him that the principle cannot with safety be depended 
upon, when used for early forcing. Of brick pits, perhaps it may be said, these 
difficulties are removed, yet the general objections to them are, the expense 
incurred in building them, and the quantity of dung required to raise and keep 
a proper degree of warmth; but the greatest is, that the structure is fixed, and 
is a perpetual habitation of wood-lice, or milepedes. These pits, however, have 
various good qualities, which are well described by Mr. Macphail. The first and 
greatest of these is, “ that the coldest place in the bed is exactly in the centre of 
each pit; plants being planted in this centre or coldest part of the bed, their 
roots can never be hurt by the heat increasing on each side gradually, being in 
every respect suitable for their increase and extension. The heat in the centre 
of each pit where the plants are first planted seldom rises higher than to about 
eighty or eighty-five degrees, nor does it ever rise higher in any of the pits than 
about ninety-six or ninety-seven degrees, nor do I believe,” he says, “it ever can 
be raised higher than that, without searching by top-heat or heated air.” Here 
Mr. Macphail is mistaken. “ Whereas in a bed made of dung, the heat in the 
centre of the bed under the mould in which the plants are planted, frequently 
rises to above one hundred and twenty degrees, when at the same time, the air 
in the frames can scarcely be kept up to a proper degree of heat.” This passage 
from Mr. Macphail is cited as corroborative of the fact, that a very strong bot- 
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