250 ON PROTECTING EXOTIC PLANTS THROUGH THE WINTER SEASON. 
depth according as the plants are bulbous, herbaceous, or shrubby. The latter 
will, of course, require a considerable depth of soil, while, for the former, a shallow 
and well-drained compost is indispensable. 
In appropriating a plot of this description to the above purpose, one of the 
most obvious difficulties is to select plants to which such circumstances are at all 
suitable. It is well known that exotics, particularly evergreen ones, are frequently 
injured, even in greenhouses, on account of the insufficient supply of light which 
our climate affords them in the winter season. In how much greater proportion, 
therefore, must this injury be experienced where light is necessarily almost wholly 
excluded ! To meet this difficulty, great and constant attention will be required 
on the part of the cultivator ; and whenever the atmosphere is dry, and above 
freezing point, the whole of the covering must be temporarily removed. To effect 
this, pulleys may be attached to the top of the erection, by which the canvass may 
be allowed to slide off when the weather is favourable. By admitting air and 
light only at the sides, great good will be effected, but by occasionally allowing the 
plants a few hours of full exposure, more advantage will be derived than would 
result from their being only partially uncovered at the sides for as many days. In 
regulating this degree of exposure, the state of the external atmosphere, as regards 
humidity or dryness, should be as much attended to as its temperature ; for, as we 
have frequently had occasion to remark, excessive dampness is as prejudicial to 
exotic plants as frosts in the winter months. 
Deciduous plants and shrubs are unquestionably the least injured by being 
secluded from light through the winter, as, at this period of their growth, they 
are naturally in a state of torpidity, and their parts require no stimulus from 
solar influences to enable them to perform their proper functions. But even to 
these a slight degree of exposure is necessary, since, by constant confinement, their 
buds would be prematurely developed, and, by a necessary consequence, would 
either perish or produce their leaves and flowers in a very imperfect state. To 
evergreens, on the other hand, too much light cannot be admitted ; for, if their 
leaves are once permitted to assume a sickly or yellow hue, they will never regain 
their natural colour, and will probably wither on their first exposure to solar 
light, to the manifest injury of those subsequently produced, and of the whole 
plant. 
This mode of treatment is peculiarly adapted to bulbs, on account of the winter 
being their period of rest; and, in the opinion of the Hon. and Rev. William 
Herbert, a gentleman who has applied his great talents almost exclusively to the 
examination and cultivation of this class of plants, many of those species which 
are usually cultivated in the stove, would succeed admirably in such a situation as 
that we are now considering, provided they could be furnished with a slight 
bottom heat in the summer ; which might be effected either by subterranean 
flues or hot-water pipes. These latter, or rather the heat with which they are 
supplied, might be devoted to other purposes in the winter, as nothing further 
