Few things have more perplexed gardeners Chan the different degree in which the same species of plant has been affected by frost in the same locality. The last two winters have afforded abundant examples of plants destroyed and unharmed in the same garden or village, under what have been thought to be identical circumstances. Many of these cases have appeared to be so little explicable by differences of temperature, that he who Would interpret such phenomena has been obliged, in some instances, to assume that different individuals of the same species possess different degrees of vitality, which renders some more able than others to resist a low temperature.

We find in the "Revue Horticole" some valuable observations upon this point, by M. Charles Martins, who has very carefully studied as a physicist* the effects of the last two winters at Montpelller. Without denying that the vital power of individuals differs considerably, he has nevertheless sought to explain the phenomena which were presented to him by reference to mere differences in temperature; and we cannot do better than give a concise account of the result of his inquiries.

In the first place he points out the great differences in temperature which are known to occur in places quite contiguous to each other, but which are unsuspected by the ordinary observer. By way of illustration be takes some details supplied by M. Renou from Vend6me in 1852. The valley of Huchingy, about a mile and a half from that place, is 200 yards wide, and bordered by little eminences only 40 yards high. In this place it is always found that the winter temperature, when the wind is in the north, is from 5.° to 15° lower than at Vendome. For instance, Jan. 24, 1852, the temperature at Vendome was 26°, and at Huchingy at the same hour 21°. Feb. 21, Vendome 26°, Huchingy 19°. March 4, Vendome 28 1/2, Huchingy 17 1/2°. Finally, on the 20th of April, while the air of Venddme was 30o, the thermometer fell at Huchingy to 15°. Such differences; he remarks, are the necessary consequence of the laws of heat, and it would be most surprising if they did not exist An observer of the weather who should announce his having remarked the same temperature in the centre and environs of a town, on the north and south sides of a nil], in a low place and on a height, would gain little credence from those who understand these subjects.

Gardeners are most especially those who should appreciate and provide against such differences.

* This word has been lately proposed as the English form of the French word physicien, and we willingly adopt it.

As an example of their effect, M. Martins cites the following instances, which occurred this last spring at Montpellier to the. Sweet Bay, Olive trees, and Fig trees, Of these plants some perished while others escaped, and it was here that the effects of aspect and shelter were most conspicuous. In fact, had not the ordinary thermometers shown that the minima of temperature greatly differed, these trees - real living thermometers as sensitive as those of the philosophical instrument maker - would have plainly indicated it.

To begin with the Bay. In a low part of the Botanic Garden, where the temperature was ascertained to have been 4- 3° on the north side of a wall, and - 1° away from all shelter, the Bays almost all died. But it was different in a part of the gardem called the Bosquet de Narcisse, where a swell of the ground raised the surface about six yards; here the Bays suffered little; a few were scorched, bat the foliage of most of them remained green. At this place the thermometer did not fall lower than + 6 1/2o. Undoubtedly, in the Bosquet de Narcisse the Bays were sheltered by high Cypresses and great Gettises; but in a neighboring garden they suffered very little, although not at all sheltered. Moreover, in the low part of the garden the Bays died, although they were sheltered. In short, they escaped wherever there was any rise of the ground., Hence it appears that the difference of a few yards in the level affects temperature so much as to produce entirely different effects upon vegetation. M. Martins remarked, however, that Bays stronger than the rest escaped the frost in the midst of others that died.

It was the same with the Olive trees.. In low places where the thermometer fell to - 1° they perished down to the old limbs. In a place protected from the north by a house they only lost their leaves. In all the district between Montpellier and Nismes the Olive trees of the plain suffered .more or less, and had to be cut back, while those on the low hills sustained no injury. None of these hills are above sixty yards high, and many much lower. There was a pair of young Olive trees (Olivettes) planted near each other, but with a difference of elevation between them of ten yards only; in one the leaves were all scorched, in the other they were scarcely hurt. Many coses of the same kind were observed in other places. These facts appear to establish a general law that " cold is most injurious in low places where radiation is most intense in consequence of the tranquillity of the air, and least injurious in exposed places where the agitation of the air opposes the effects of radiation".

Fig trees and Pomegranates presented the same general results.

Hence M. Martins infers that one of the first duties of a gardener is to make himself acquainted with Local climates, the differences among which are far greater than is generally imagined. For example, there occur in the Botanical Garden of Montpellier no fewer than four local climates. I. The coldest in winter and hottest in summer; this is the lowest place unsheltered to the north and west, and only protected to the east by some tall trees. 2. A space to the north of this, protected by houses and walls; it is not so cold, but as hot as the first 3. The Botanical arrangement, sheltered on the north by an Orangery and greenhouse, surrounded by trees and buildings, and overlooked on the south-west by the hill du Peyrou; this is not so cold in winter, but excessively hot in summer. 4. The Bosquet de Narcisse and other elevated places; here the climate is more equable, less cold in winter, less hot in summer. The mildest place of all is the south slope of a little artificial mound, occupied by evergreen Oaks, Aleppo Pines, Loquats, etc.

These circumstances appear to be deserving of notice, for they show that in addition to the well-known protection afforded by walls and aspects, a very important practical effect is produced by such slight elevations as even a few yards; a point too often-very little attended to in forming a garden, and very possibly the cause of some of the apparently conflicting results obtained by those who have recorded the effect of cold upon exotic trees. Host especially are they important as demonstrating the fallacy of thinking that a place is warm in winter because it is low, and cold at the same season, because it is high. The defect of M. Martins' observations seems to us to consist in his taking no account of the drainage of the places described by him.