Let us now inquire what means appear best calculated to meet the several contingencies to which we have referred; and how far it appears to be within our control either to remedy or to avoid them.

The class of injuries to plants resulting from heat are practically much better within the control of the gardening world at large than those arising from cold; because they are principally such as occur either from want of care in, or from the ignorance of, the cultivator. Such are the burning of Slants in hotbeds, and the injurious effects produced by overheated plant-ouses. The remedy in reference to hotbeds is of course easy enough, namely, more care in future. But as regards over-heated plant-houses, a word of caution may not be out of place. One effect of it, the evil of keeping them at too high a temperature for the purpose to which they are applied, is, to prolong injuriously the period of the annual growth, by keeping up an undue excitement of the energies of the plants; and the consequence of that invariably is, that this new growth does not mature sufficiently, and whether for flowers or for fruit, a diminution of the quality of the crop results; and, in addition, an exhausted state of the plants ensues which is sure to enfeeble their powers of production the following year; and in some cases for a much longer period, even on the assumption that the error committed is in future avoided.

A caution on this point also may be added, namely, that whenever it is discovered that plant-houses are, or have been, kept overheated, the return to a proper but lower temperature must be effected gradually, and not suddenly. Thousands of plants have been destroyed from inattention to this remark.

When we turn, however, to the class of injuries to vegetation resulting from extremes of cold, we approach a part of our subject in which every lover of horticulture in these latitudes feels a deep interest, whatever be the branch of it to which his attention is directed. The fruit-grower laments over his trees, the arboriculturist over his tender evergreens, the florist over his numberless rarities, and the market gardener fails not to enhance the value of his early vegetables by lamentations over his losses, real or imaginary, but too often the former.

In order to take some general view of this branch of our subject, it will be best to consider it in reference to some of the practical details in which we every winter meet with it in the ordinary course of the requirements of a gentleman's country residence; for there we too often find it operating unfortunately, notwithstanding the efforts of an intelligent gardener, to the prejudice of every department under his care. For although his skill and care may, and usually do, avert serious injury from this cause in the performance of his varied duties, yet in numberless ways he is compelled to refrain, from this cause alone, from many operations which, but for it, he would lay his hand to, and to lament that expense on the one side, or incapability of climate on the other, preclude the possibility of his carrying out many a vision which his imagination pictures, and which, under other circumstances, he possesses the needful knowledge and ability to realize.

We have above adverted to the effect of frost upon the organization of the tissue of plants. Experience has shown that, where the intensity of the freezing process has not been sufficient to rupture the vessels to any considerable degree, the elasticity of the fibre will preserve the plant from injury in numerous cases, if not in all. But it is found that, to attain that result, the plant must be thawed very gradually, for if the thaw is sudden there is much greater danger of injury. Why this should be so is not precisely apparent, beyond the assumption that it is connected with the necessity for the elastic principle to be brought into play as evenly as possible throughout the whole structure of the plant that has become rigid from the effects of frost.

The great object, therefore, in the recovery of plants from the effects of frost, is, to remove the frozen condition as gradually as possible, and to guard them against sudden exposure to heat, and from the direct influence of the sun.

In plant-houses this can be effected by shading the roof, and by syringing the plant with very cold water; taking care, at the same time, that no fire heat is present that will raise the temperature of the house more than a very few degrees above the freezing point. If that course is persevered in for several hours (the syringing being repeated) until the plants assume their natural appearance, it will preserve hundreds that otherwise would have been killed; although, of course, if the frost has been intense, many species may have become injured beyond remedy.

In reference to this subject, (the syringing of frozen plants,) we speak with confidence from experience, and experiments made specially to test the correctness of the principle, many years ago, with plants subjected to several modes of treatment. And we advert to it specially, (although an old remedy,) because we were surprised recently to have its accuracy questioned by a practical man who is undoubtedly a good gardener. Nevertheless, we are satisfied that if the conditions we have specified be observed, (namely, keeping down the temperature to only just above the freezing point, and shading,) this plan is most valuable. Any one who doubts it has only to subject half a dozen plants of a succulent kind (such as the geranium) to several degrees of frost, and then, when quite stiff, to place some of them in a warm room, and let the others lie twenty-four hours with their entire heads immersed in a tub of cold water in a cool cellar, and the result will show the efficacy of removing frost by the mode recommended.

For out-door trees and plants when frozen, shading is perhaps the best method within our power to adopt; the principle, of course, is the same, namely, to let them thaw as gradually as possible. When covered with snow, nothing can be better. But with tender plants it will be well to cover the snow over them with straw or mats, so that the sun may not act directly upon them, and the thawing process be thereby rendered more gradual.

It is well known that many trees and shrubs that are found to be tender in a particular latitude, when placed in a southern aspect, will, notwithstanding, endure the severity of winter when planted on the north 6ide of a fence or wood, so as to be screened in a great measure from the sun's direct rays. This, of course, depends on the same principle, the less sudden nature of the changes of temperature that take place in such a situation.

There is much reason to suppose, also, in regard to the effects of frost upon vegetation, that the alternation and repetition of the action of frost and thaw upon it during any given period, is much more prejudicial than the continued duration of the same degree of intensity of cold, lasting over an equal consecutive number of days. This possibly arises from the greater interference with the organization arising from the increased action that is called for in the adaptation of the elastic principle before adverted to, to the exigencies of the changes of temperature. Hence arises a reason for care in guarding, as far as practicable, against the attack of frost; and for watchfulness in the replacing of coverings, when temporarily removed, in winter, to plant structures of all descriptions.

Much diversity of opinion exists among practical men as to the advantage or otherwise of protection by straw or other covering to trees and shrubs in the open ground that are somewhat tender. Where the risk is slight only, (according to the species of plant,) we are inclined to run it, in preference to covering. But when there is no question about the tender nature of the plant, then there is no alternative but to have recourse to it. As to the mode to be adopted for deciduous plants, straw neatly bound round them is as good, and possibly as little offensive, as anything. But for evergreens an old barrel or slight wooden structure is the most effective, although not very ornamental.

Whenever out-door coverings are used, they should not be removed too early after the winter, because the plant will be more susceptible of changes of temperature then than it would have been if left exposed to the full action of the weather.

We do not assume that these remarks will be of value to the practical man, but we trust the novice in horticulture may find some benefit from attention to them.

[The preceding article is a suggestive one, and if it were not already so long, we should add here some reflections as to how far the temperature may be carried consistently with the health of the plant, and in furtherance of the specific object in view in cultivating some particular kinds of plants: this we shall do at some future time. At present, however, we wish to endorse emphatically all that B. M. says in regard to the treatment of frozen plants. We have tried it many times, and with entire success. LTreference to the protection of out-door plants, we believe that in many cases more injury is sustained by too much covering, than by the severity of the weather; and often plants are covered that do not need any protection. B. M.'s remarks on this head are timely and to the point. - Ed].