warmly for a few hours and dissolves the snow which had lodged upon the plants on the south side of a wall or house: at night, the moisture is frozen on their leaves and stems, and the plants suffer from the violence of the transition from heat to cold.
It is well observed by Mr. Knight—a gentleman who, by his patient investigation and very delicate and ingenious experiments, has contributed more than any other individual in this country, since the time of Hales, to enlarge our acquaintance with the physiology of vegetation; that part of botany by far the most interesting and most instructive, and indeed without which it must be considered as little better than a dry and barren nomenclature, unworthy to be ranked among the sciences;—It has been well observed by Mr. Knight, that it is from attending to the effect of temperature on plants in different states of irritability that early fruits are to be obtained, the influence of climate on the habits of plants depending much less on the aggregate quantity of heat in any climate than on the distribution of it in different seasons. He conjectures, and not without plausibility, that if two plants of the vine, or other tree of similar habits, even if obtained from cuttings of the same tree, were placed to vegetate during several successive seasons in very different climates; if the one, for instance, were planted on the banks of the Rhine, and the other on those of the Nile, each would adapt its habits to the climate in which it was placed; and if both were subsequently brought in early spring into a climate similar to that of Italy, the plant which had adapted its habits to a cold climate would instantly vegetate, whilst the other would remain perfectly torpid.
The irritability of plants is unquestionably increased by the subduction of heat: vines in grape-houses, which have been exposed to the external air and all the cold of winter will become forwarder and more vigorous at spring than those which have been confined within the warm atmosphere of the house throughout the winter. Onions, potatoes, barley, &c. &c. will vegetate with a less degree of heat in spring than in autumn: roots introduced from southern latitudes germinate earlier in the season than those brought from more northern ones, retaining under different circumstances the habits they had previously acquired. Apple trees sent from this country to New England blossomed for a few years too early for that climate, and bore no fruit; but afterwards learned to accommodate themselves to their new situation. (See Bot. Garden, Part II. Cant. I. p. 322. Note on the Swallow.)
Mr. Knight, in a communication to the Transactions of the Horticultural Society, (No. I.) says he has found that the crops of wheat on some very high and cold ground which he cultivates
