of its superior gravity, descends and displaces the warm air of the valleys; yet the sugar-canes are so far from being injured by this decrease of temperature, that the sugars of Jamaica take a higher price in the market than those of the less elevated islands, of which the temperature of the day and night is subject to much less alteration. At Fattehpúr, in the East Indies, the difference in temperature between night and day amounts to as much as 78°, on an average of the whole year; in April the greatest heat by day is 110°, that of night is only 65°; in January the thermometer falls to 38° at night, while the day is 76°; and there are 40 degrees of difference between the day and night in May, one of the hottest months, when the thermometer ranges as high as 115°. At Calcutta, in May, the thermometer averages 93° in the day, and 79° at sunrise; while in January the temperatures are 77° and 56° respectively, for those two periods.

When we compare these facts with the habits of plants just adverted to, we must, I think, see that it is the purpose of nature to reduce the force which operates upon the excitability of vegetation at that period of the twenty-four hours, when, from other causes, the powers of digestion and assimilation are suspended. As far as is at present known, that power is heat; and therefore we must suppose that, to maintain at night in our hot-houses a tem

perature at all equal to that of the day, is a practice to be much condemned. Plants will no doubt lengthen very fast at night in a damp heat, but what is at this time produced seems to be a mere extension of the tissue formed during the day, and not the addition of any new part; the spaces between the leaves are increased, and the plant becomes what is technically and very correctly called drawn; for, as has been justly observed, "the same quantity only of material is extended to a greater length, as in the elongation of a wire."

Mr. Knight has pointed out another ill effect of high temperature during the night, namely, that it exhausts the excitability of a tree much more rapidly than it promotes its growth, or accelerates the maturity of its fruit; which is, in consequence, ill supplied with nutriment at the period of its ripening, when most nutriment is probably wanted. The muscat of Alexandria, and other late grapes, are, owing as he thinks to this cause, often seen to wither upon the branch in a very imperfect state of maturity; and the want of richness and flavour in other forced fruits is often attributable to the same cause. "There are few peach-houses," he adds, "or indeed forcing-houses of any kind, in this country, in which the temperature does not exceed, during the night, in the months of April and May, very greatly that of the warmest valley in Jamaica in the hottest period of the year. There are pro

bably, as few forcing-houses in which the trees are not more strongly stimulated by the close and damp air of the night, than by the temperature of the dry air of the noon of the following day. The practice which occasions this cannot be right: it is in direct opposition to nature." In the same paper from which the foregoing is an extract (Hort. Trans., ii. 135.), the same great experimentalist records the result of his own management of a peach-house, where a due regard was had to the preservation of a sufficiently low temperature at night. "As early in the spring as I wanted the blossoms of my Peach trees to unfold, my house was made warm during the middle of the day; but towards night it was suffered to cool, and the trees were then sprinkled, by means of a large syringe, with clear water, as nearly at the temperature at which that usually rises from the ground, as I could obtain it; and little or no artificial heat, was given during the night, unless there appeared a prospect of frost. Under this mode of treatment, the blossoms advanced with very great vigour, and as rapidly as I wished them, and presented, when expanded, a larger size than I had ever before seen of the same varieties; which circumstance is not unimportant, because the size of the blossom, in any given variety, regulates, to a very considerable extent, the bulk of the future fruit."

CHAP. XX.

OF SOIL AND MANURE.

NOTWITHSTANDING all that has been written upon these substances, and the endless accounts we possess of their real or supposed action upon vegetation, I must confess that the contradictions are so numerous, the exceptions to supposed rules so frequent, and physiology is so insufficient to account for the greater number of well ascertained facts, that it does not appear to me possible to construct any tolerable theory relating to them.

Mr. Knight has observed that varieties of the same species of fruit tree do not succeed equally in the same soil, or with the same manure: the Peach in many soils acquires a high degree of perfection, where its variety, the Nectarine, is of comparatively little value; and the Nectarine frequently possesses its full flavour in a soil which does not well suit the Peach. The same remark is also applicable to the Pear and the Apple; and, as defects of opposite kinds occur in the varieties of every species of fruit, those qualities in the soil which are beneficial in some cases will be found injurious in others. In those districts where the Apple and Pear are cultivated for cider and perry, much of the success of the planter is found to depend on his skill or good

fortune in adapting his fruits to the soil. (Hort. Trans., i. 6.) Rhododendrons and Kalmias are usually cultivated in peat earth mixed with sand, and yet they grow as well in fresh hazelly loam, without any mixture whatever; and, than these two kinds of soil, none can be apparently more dissimilar. The fine American cottons are grown in a calcareous sand, those of India in a deep black saponaceous earth: the American cotton will not thrive in the latter, nor that of India in the former, as has now been ascertained; and yet the species of Gossypium producing the two qualities have no organic differences which can, so far as has yet been ascertained, explain in the smallest degree the necessity, under which it is evident that they labour, of being provided with different kinds of food. The Alnus glutinosa, or Common Alder, flourishes in wet clayey meadows; while Alnus incana, or Upland Alder, is equally suited to a dry and light land: we are totally ignorant of the reason of such a case as this. Rhododendron hirsutum and Erica carnea are, in their wild state, confined to calcareous soil; while Rhododendron ferrugineum grows exclusively on granite, and Erica vagans on serpentine. We are informed by Beyrich (Gardener's Magazine, iii. 442.) that " the Pine-apple, in its wild state, is found near the sea-shore; the sand accumulated there in downs serving for its growth, as well as for that of most of the species of the same family.