REQUIRE COOL NIGHTS.

521

the most luxuriant verdure of leaf up to this time, then sickened and died, every leaf falling off. Euphorbia jacquiniflora lost all its leaves, but the Stephanotis was not materially injured.

On the other hand, Mr. Spencer, another of our great gardeners, has had to manage a house at Bowood, which, though generally called a stove, and filled with stove plants, is never kept during the winter months at a higher temperature than from 40° to 50° by fire heat. The plants are principally used for decorating rooms, and for this purpose late flowering plants are mostly cultivated. The roof is partially covered with creeping stove plants, including Combretums, Bignonias, Passifloras, Stephanotis, &c. The effect of this low temperature on these and similar plants is to produce not only an entire cessation from growth in winter, but in some cases they become partly deciduous, and he found that they bore this low degree of heat not only without injury, but when the warm days of spring returned they broke with unusual strength and vigour, enjoying as they do, in fact, almost a natural climate. It is generally thought Bignonia venusta will not bloom freely except it grows in bottom-heat. That plant grows in a border inside this house, without having any bottom-heat beyond what the house affords, which, during the autumn and winter, is necessarily very low; and yet the plant is every season covered with bloom for two or three months. Stephanotis blooms equally well in July, and the Combretums and Passifloras nearly throughout the year. Echites splendens blooms equally well in the summer, and he finds the flowers of a much higher colour than those from plants grown in a warmer house; in the winter Echites becomes a deciduous tree.

The same result was obtained at Drayton Manor, where, in a Vinery, Pergularia odoratissima, Echites splendens, Stephanotis floribunda, Bignonia Chamberlayniæ, Combretum purpureum, and Clerodendron volubile were planted in the year 1847 against the back wall, and where they grew in the greatest vigour. Mr. Milne's account of their treatment is this:-"When the stove climbers were planted on the back wall of the Vinery, it was with the understanding that they should receive the same treatment as an early Vinery requires, and live or die. At the same time what could be done was done for them, in order to preserve them through the winter; water was withheld from them after September, in order to induce rest before the dead of the year. No particular attention was paid to the thermometer in the house, few fires were used in the winter, and the temperature of the house was frequently as low, in the mornings of frosty nights, as 35°, and on one occasion 32°, when the earth in watered pots in this house was frozen; no fire was made to thaw, but they took their chance. The house was fully opened on all mild days, and partially so every day during the winter. The temperature of the earth about their roots was not always measured, but it is known to have been 58°, and in the absence

522

THESE FACTS ILLUSTRATE

of all moisture it may have indicated not less than 50° in January. The most difficult period to deal with those climbers was found to be the time of starting. In a short time after the application of heat they began to exhibit some signs of debility, but a low night temperature (40°), and water withheld still, overcame this small difficulty. Similar results were obtained by Mr. D. Beaton, and others.

Upon the right understanding of these great facts depend all the details of forcing, which is never successful unless the habits of a plant in a wild state are carefully followed. By way of illustration, the case of the Strawberry may be taken as a very common and well understood plant, from which, however, unskilful gardeners obtain no crop when forced, although, as they say, they give it plenty of heat, shut it up close at night, and expect to gather ripe fruit from it in six weeks. They evidently do not consider how it is that the Strawberry is made to bear fruit naturally. The cold of winter does not suddenly change to the heat of the dog-days. Warm dew does not incessantly bathe the rising herbage. The nights of spring are not more oppressive than the days. In short the climate in which the Strawberry naturally delights is not in the smallest degree like that which is provided for it. On the contrary, where the Strawberry dwells the temperature rises very slowly, and at about the same rate as light increases; if one day is warm another is cold, and the nights are always so; the air, too, is dry more often than damp-as will be evident if we bear in mind how ceaselessly the east wind breathes upon the land of Strawberries. Three long months of steady growth are required to produce the Strawberry under these favourable circumstances. It is therefore folly to imagine that in six weeks the same end is to be accomplished by unnatural means. We may assist Nature, we cannot compel her. What is true of the Strawberry is equally so of all other forced productions, whether fruits or flowers.

Knight pointed out as one of the ill effects of high temperature during the night 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

THE TRUE PRINCIPLES OF FORCING.

523

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. The same great experimentalist records (Hort. Trans., ii. 135) 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." It is, however, proper to add that the observations of Knight referred to a period when the principles of gardening were not generally understood so well as they now are.

The preceding remarks apply exclusively to plants in a state of growth. When growth ceases and fruit begins to ripen, circumstances in some instances wholly change.

In its favourite regions the Grape ripens its fruit at the hottest and dryest period of the year. In Corfu the Grapes are ripe in September. It appears from Dr. Davy's observations that the range of the thermometer in that island, day and night, is in August from 77° to 84°; and in September from 74° to 82°; that is to say, it is never colder at night than 74° in September, or than 77° in August. At Malta the lowest temperature observed in August was 74°; and in September 69°. In Candahar, Mr. Atkinson found Grapes ripe in June. The night temperature of Candahar in May and June is not given; but we may be very sure that in a country like

524

RIPENING FRUIT REQUIRES WARM NIGHTS.

that, where a burning sun has been shining for three months, and the ground is excessively heated, there must of necessity be a very high temperature at night. In fact, in Persia, which is nearly the climate of Candahar, the midnight temperature of August has been known to be as high as 108°; and it is certain that in all such countries the difference between the temperature of the day and night, at the hot season of the year, when Grapes ripen, is inconsiderable. We may, therefore assume that a night temperature of from 70° to 80° ought to be secured when Grapes are ripening.

At that period of their existence much atmospheric moisture is unnecessary, or rather injurious to Grapes, for it will inevitably cause the Vine to break into a multitude of little branches to the impoverishment of the fruit. In the Vine countries the air is parching; Mr. Atkinson's paper curled up in Candahar, while he was writing on it; and the Vine will bear such a climate well, if it is gradually inured to it, provided the roots are in a moist soil, and there is a free circulation of air. It is to be recollected that when a tree is ripening its fruit, it is in quite a different condition from what occurs when it is flowering. At the latter period its energies are all directed to organizing itself, and consolidating the parts that may have been formed; it is growing, and hardening its growth. But at a later period organization and consolidation are accomplished, and it is the elaboration of the fluids, stored up within the plant, that has to be provided for. The fruit of such a plant as the Vine is incessantly sucking fluids out of the branches; but that fluid is little more than water and mucilage. It is after reaching the fruit that it thickens by evaporation, and changes owing to chemical combinations brought about by a variety of phenomena; the result of which is the conversion of acid into sugar, and the creation of the delicate flavours which give the Grape its value as a fruit.

CHAPTER XX.

OF SOIL.

THE word soil signifies that portion of the crust of the earth in which plants grow; what lies below it is rock. It is to a great extent formed by the wearing down or decomposition of rock, with the addition of matters derived from the action of plants and animals, and from their decay. Soil, therefore,

consists of two kinds of matter arising from different sources: one formed by the decay of rock is inorganic; the other originating in living things is organic. Clay or loam, sand, lime, and all the earthy or alkaline matters found associated with them, are inorganic. Peat, mould, and every thing which is convertible into these two substances, is organic. The supposed action upon vegetation of these kinds of matter has been scientifically investigated by all modern writers upon rural chemistry, to whose most valuable labours the reader in search of chemical facts will have recourse. In this place they will be regarded merely from a practical point of view.

CLAY is a dense, plastic substance, pasty when wet, abounding in iron, tenacious of water, hardening and cracking when long exposed to dryness, and having the power of condensing ammonia and other gaseous matters. Its peculiar properties are chiefly owing to its containing alumina, a substance incapable, when pure, of supporting vegetation. In cultivated land clay always occurs mixed with sand or chalk, or both, in variable proportions. Heavy clay contains about 20 per cent. of sand; loam 50 or 60 per cent.; calcareous loam has a considerable quantity of lime (chalk) in addition; fibrous loam