ANNUAL REST IS UNIVERSAL.

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Clouds are seldom seen in the sky; the heat of the sun is only rendered supportable by the sea breeze, which blows regularly from the south-east during the greater part of the day. The nights are calm and serene, the moon shines more brightly than in Europe, and emits a light that enables man to read the smallest print; its absence is in some degree compensated by the planets, and above all by the luminous effulgence of the galaxy. From the middle of August to the end of September, the thermometer rises frequently above 90°, the refreshing sea breeze is then interrupted, and frequent calms announce the approach of the great periodical rains. Fiery clouds are seen in the atmosphere, and the mountains appear less distant to the spectator than at other seasons of the year. The rain falls in torrents about the beginning of October, the rivers overflow their banks, and a great portion of the low grounds is submerged. The rain that fell in Barbadoes in the year 1754 is said to have exceeded eighty-seven inches. The moisture of the atmosphere is so great, that iron and other metals easily oxidated are covered with rust. This humidity continues under a burning sun; the inhabitants (say some writers) live in a vapour bath." (Malte Brun's Geography, vol. v. p. 569, Eng. ed.)

It is evident, from what has been said, that the natural resting of plants from growth is a most important phenomenon, of universal occurrence, and that it takes place equally in the hottest and the coldest regions. It is, therefore, a condition necessary to the well-being of a plant, not to be overlooked under any circumstances whatever, and there cannot be any really good gardening where this is not attended to in the management of plants under glass. Rest is effected in one of two ways, either by a very considerable lowering of temperature, or by a degree of dryness under which vegetation cannot be sustained.

The way in which the physical powers of vegetation are affected by this has been already explained, and in practice it is found a point of the utmost consequence. The early fruitgardener draws his Vines out of the vinery, and takes the sashes from his Peach and other forcing-houses, when the

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EFFECTS OF ANNUAL RESTING.

artificial season of growth is over, in order to prepare them for the duty of a succeeding season; although this operation is performed in summer, its effect is to expose them to dryness, which arrests their growth, and favours the deposit in their wood of the matter required for the produce of a succeeding

year.

The effects of a very dry atmosphere are necessarily an inspissated state of the sap of the plant, and this in all cases leads to the formation of blossom-buds and of fruit. It thus operated upon some Pine-apple plants in Mr. Knight's garden, to such an extent as to cause even the suckers from their roots to rise from the soil with an embryo Pine-apple upon the head of each, and every plant to show fruit, in a very short time, whatever were its state and age. Very low temperature, under the influence of much light, by retarding and diminishing the expenditure of sap in the growth of plants, comparatively with its creation, produces nearly similar effects, and causes an early appearance of fruit.

The operations of forcing are essentially influenced by these facts; and, by a skilful alteration of the periods of rest, we are enabled to break in upon the natural habits of plants, and to invert them so completely that the flowers and fruits of summer are obtained to load our tables even in winter. Of this, the following instance, taken from a paper by Mr. Knight in the Horticultural Transactions (vi. 232), is a sufficient illustration.

"A Verdelho Vine, growing in a pot, was placed in the stove early in the spring of 1823, where its wood became perfectly mature in August. It was then taken from the stove and placed under a north wall, where it remained till the end of November, when it was replaced in the stove, and it ripened its fruit early in the following spring. In May it was again transferred to a north wall, where it remained in a quiescent state till the end of August. It then vegetated strongly, and showed abundant blossom, which, upon being transferred to the stove, set very freely, and the fruit, having been subjected to the influence of very high temperature, ripened early in the month of February."

The Strawberries of February and March are in like manner

SEASON OF FLOWERING MAY BE CHANGED.

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procured by exposing the plants to such an amount of dryness and heat as can be obtained by presenting them unwatered, in pots, to the sun at an early period of summer, so as to cause a sufficient accumulation of excitability by the end of autumn, instead of the month of May.

It must be manifest that the operations of the flowergardener should be regulated by the same principles, although it may be confessed that they are often little considered; a circumstance the more strange, from the indispensable necessity of resting fruit-trees being universally known. It is to the giving their plants the proper kind of rest that some gardeners owe the magnificent blossoming of their Chinese Azaleas, Cacti, Camellias, and other forced flowers, much more than to any peculiarity in the compost they employ, which is often a point of subordinate interest, although often regarded as of the first importance.

If little progress has been made in altering the time of flowering of particular races, so as to invert their seasons, this is certainly far from being beyond attainment; and there is no more reason why a Chinese Chrysanthemum should not be compelled to flower at midsummer instead of November, or a Dahlia at Christmas, than that Vines and Strawberries should ripen fruit in February. The great difficulty to contend against in obtaining winter flowers is want of light and free access to air; but, by the employment of slender iron sashbars and large glass, a sufficient amount of light may be obtained in England even at that season of the year; it is in the free admission of warm moist air that gardeners are deficient (see pages 213, &c.).

It is well known that plants from the northern half of the world, when they have become naturalised in the south, have changed almost entirely the time of their vegetating, blooming, and fruit-bearing, so as entirely to accord with the habits of the indigenous plants of the country. Thus we find that at the Cape of Good Hope, Oaks, Alders, the Almond, Peach, and Apricot, are in full bloom in August.— Treviranus.

But it is not merely the periodical rest of winter and summer that plants require; they have also their diurnal repose: night

L L

514

NIGHT TEMPERATURE MUST BE

and its accompanying refreshment are as necessary to them as to animals. In all nature the temperature of night falls below that of day, and thus one cause of vital excitement is diminished; perspiration is stopped, and the plant parts with few of its aqueous particles, although it continues to imbibe them by all its green surface as well as by its roots; the processes of assimilation are suspended; no digestion of food and conversion of it into organized matter takes place; and, instead of decomposing carbonic acid by the extrication of oxygen, they part with carbonic acid, and rob the air of its oxygen; thus deteriorating the air at night, although not to the same amount as they purify it during the day. It is, therefore, most important, that the night temperature of glass houses should be lower than that of the day. We are told that in Jamaica and other islands of the West Indies, the air upon the mountains becomes, soon after sunset, chilled and condensed, and, in consequence 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 from 38° to 45°; 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.

But it is not merely in the tropics that this great diminution of temperature at night takes place; it is universally the case in all climates whence our fruit-trees have been derived. When we consider how clear the sky is in the lands of the East, it is impossible that there should not be a great amount of nocturnal radiation, the effect of which will necessarily be to cool down the air to a very considerable extent, especially in the spring. If we look to the registers of temperature

LOWER THAN DAY TEMPERATURE.

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kept in such countries, that which was before a matter of inference becomes established by direct evidence. Take Malta as an example: in the month of January, according to Dr. Davy, the thermometer reaches 60° in the day, but falls to 42° at night; and even in July, the difference between the day and night amounts to 16°. In the Ionian Islands, Zante, Corfu, Cephalonia, fine Grape countries, the difference is not less considerable. Nevertheless, many gardeners, when they begin forcing early Grapes, quite neglect this important fact. With some it is a maxim to keep the thermometer above 60° at night. But what does nature do where the Vine thrives best? In Zante, whence come the Currants, or Corinth Grapes of the shops, the Vine pushes in March; and it is a common saying there, "that after the 10th March (Old Style), not even a dog without a tail should be allowed to enter a Vineyard," (Davy's Ionian Islands, ii. 345) because of the risk of his breaking off the young and tender shoots. Now the average temperature of Corfu, at 8 A.M., in the month of March, we learn from the same authority, is only 51°; and of course it must have been some degrees lower during the night; in April it is not more than 57°; and it does not reach 61° till May, when, since the Grapes are ripe in August, the berries must be set. There can be no doubt, then, that 48° is quite high enough at night for Grapes in the first month of their growth, and 54° in the second.

But there are other illustrations if we inquire into the natural history of the Grape Vine. Nowhere is the climate more sultry than in Affghanistan. We are told that General Pollock's troops at Jellalabad were forced to dig holes in the ground to hide themselves from the heat. The condition of Cabul must be much the same. At Candahar, we are informed by Mr. Atkinson that, in May, the heat of the tents was generally 110°; and at midday, in the sun, 140°. In no part of the world are the Grapes more delicious than in Candahar and Cabul. On the 30th June, this traveller saw donkeys laden with panniers of fine purple Grapes; and at the same time, the paper on which he was writing curled up and became as crisp as if it was before a blazing fire. When he reached Cabul, in August, he found the bazaar filled with delicious Grapes in astonishing profusion. But what sort of nights had the troops in the spring of the year, when the Vines were growing and flowering, and preparing themselves to bear fruit? On the 7th March, near Shikapore, two hundred miles south of Candahar, and above five hundred south of Cabul, in the Desert, we are told that the march took place in "a brilliant starlight night; frost seemed to be in the air, it was so cool and bracing; after midnight, the servants made up a blazing fire, for the north wind was blowing bitter cold, and the traveller was glad of hot brandy and water." Nevertheless, the day before, Mr. Atkinson had been grilling at Shikapore, and the march was over level plains, and not among the mountains. Two days after