LETTER VIII.

USE OF PLANT-HOUSES.--NATURE OF CLIMATES--DIFFERENT KINDS OF HOTHOUSES.--THE DRY STOVE, THE BARK STOVE, AND THE ORCHIDEOUS HOUSE.--CULTURE OF PLANTS IN THE BARK STOVE.--AQUARIUM AND WATER PLANTS.--RED SPIDER.--CULTURE OF SUCCULENT STOVE PLANTS.--CULTURE OF ORCHIDEOUS PLANTS.--THE GREENHOUSE.--THE AUSTRALIAN HOUSE, AND CULTURE OF ITS PLANTS.--THE COMMON GREENHOUSE, THE HEATH HOUSE, THE CONSERVATORY, THE ORANGERY, AND THE CAMELLIA HOUSE.--THE CULTURE OF PLANTS IN THE COMMON GREEN HOUSE.--POTTING PLANTS.--HEATHS.--CULTURE OF PLANTS IN THE CONSERVATORY.--CULTURE OF ORANGE TREES.--APHIDES.

Before I say any thing of the management of the plants in your greenhouse, I must remind you that, in order to grow plants well, it is not enough merely to preserve them from the frost, but we must imitate as well as we can their native climate: that is, the degree of heat, light, and moisture they have been accustomed to in their native country, together with the air and the soil. The latter is the easiest condition to fulfil; as, by combining different kinds of earth, we can, without much difficulty, produce a very tolerable imitation of any soil we please: but it is not so easy to give plants abundance of light and air in combination with heat; and, though we can readily give plants plenty of water, it requires some management to surround them with a moist warm atmosphere, like that they have been used to in their native woods. To meet these difficulties, buildings have been constructed, suited for the reception of plants, with various contrivances for producing heat and distributing air and moisture, and with a glass roof, front, and sides, to admit abundance of light.

These structures are what we call plant-houses; and they are not only divided into hothouses for tender plants, and greenhouses for half-hardy plants, but subdivided into various kinds to suit the various climates in which plants are found. These climates, however, are not so numerous as might at first be supposed; as it is a curious fact in the history of plants, that many of the most ornamental grow in patches in some parts of the world without being found anywhere else, as, for example, the pelargoniums or shrubby geraniums at the Cape of Good Hope. Even when the same plant is found in different parts of the world, it is generally in the same climate, though in different countries; and thus pines and firs, oaks and birches, spread like belts or zones round the globe, from Asia, through Europe, to America, almost in the same degree of latitude, making an allowance for islands being warmer than continents, and mountains colder than valleys; as you must always remember that knowing the degree of latitude from which a plant comes is not sufficient to teach its culture, unless we know also whether it grows on the mountains or in the valleys, and whether the climate of the locality is moist or dry. A plant will be soon killed by a dry atmosphere, if it requires a moist one; and it will be as much injured by being kept too hot as too cold. Furze and heath will not grow within the tropics; and the first camellias introduced into England were killed by being kept in a hothouse.

From what I have said, you will perceive that as plants will only thrive in climates suitable to them, it is not enough to have a hothouse for tropical plants, and a greenhouse for those of moderately warm countries, but that you must have three or four houses imitating different climates, if you wish to grow different kinds of plants to perfection. Philosophers who have written on the subject describe sixteen distinct kinds of climate, including our own; but, as these would be too many to imitate, gardeners are obliged to content themselves with the following kinds of plant-houses and pits.

The _dry stove_ is generally kept at a heat of from 70° to 84° in the day, and never allowed to fall below 65° at night, even in winter. It should be placed in a situation sheltered from cold winds, but quite open to the sun; as the plants grown in it require a strong light, most of them being natives of dry sandy plains, on which there is no tree high enough to cast a shade. The plants are grown in pots, which are generally placed on a frame or stage of wooden or stone shelves, so as to have abundance of air around them; and the stove is best heated by flues. The plants suitable for a stove of this kind are some of the kinds of Cactàceæ, such as the genera Melocáctus, Epiphýllum, and Cèreus, with the tender kinds of Euphórbium, Mesembryánthemum, Stapèlia, Crássula, Sèdum, Sempervìvum, and Agàve, and some kinds of bulbs.

The _bark stove_ has a brick pit filled with tan or dead leaves in the centre; and it is generally heated with pipes of hot water or steam, from 60° at night to 80° in the day; the pots in which the plants are grown being either plunged in the tan, or placed on the walls of the pit, or on a stone shelf near the glass in front. Sometimes the trees of hot climates are grown in the bark bed in the centre without pots; and sometimes there is no bark pit, but the space in the centre of the house is filled with boxes containing tropical trees. This last kind is frequently called the botanic stove, as it is most common in botanic gardens; and it is best adapted for growing palms, and other monocotyledonous plants with large leaves, such as bananas, which require abundance of air and light.

The _damp stove_, or orchideous house, is only suited for orchideous plants and exotic ferns. The heat should be from 70° at night to 90° in the day, or even more; and the house should be heated with hot flues, on which water should be thrown twice or three times a day, and hot-water pipes with open tanks; as all the plants to be grown in this kind of house require excessive heat and constant moisture. As they are also plants that love the shade, the house should have only a subdued light; and though I cannot say that I approve of the coloured glass adopted by some cultivators, as it decomposes the rays of light, and deprives the plants of a portion of the heat they would otherwise derive from the sun, yet I would certainly advise that some of those climbing plants which will grow in a moist warm climate should be trained close under the glass, to produce shade.

_Forcing-houses_ for grapes and early stone fruits are of the nature of the bark stove; and in them the pit in the centre is frequently filled with pine-apple plants, in pots plunged up to the rim in the tan; but these houses belong to the kitchen-garden, as do pits for growing pines, cucumbers, and melons.

You will thus observe that there are only three distinct kinds of hothouses in use in British gardens, viz. the damp stove, or orchideous house, which is the hottest; the dry stove, or house for succulent plants, which is the rarest; and the bark stove, which is the most common, and which may be said to have two varieties, viz. the botanic stove and the forcing-house.

_The culture of hothouse plants_ in the _bark stove_ requires more care than can be expected from any one not a regular gardener; and, as most tropical plants are valuable in this country, I would not advise you to try to manage them yourself, as you would be very much vexed if you should chance to kill them. I will, however, give you a few general hints on the subject, if you should like to have a house of this kind.

All bark-stove plants require a great deal of water when they are in a growing state, and, as it is necessary that the water should be of the same temperature as the house, there should be either an open cistern in the house, or a cistern in the shed behind, near the furnace, and communicating with the house by a pipe. The best plan is to have a cistern in the house, as it can be used as an aquarium; and there are many beautiful tropical aquatics, such as the different species of Nymphæ'a and Nelúmbium, which deserve growing for their beauty, while others are interesting for their curiosity, such as the Papyrus. In summer, bark-stove plants require very little care, except to prevent them from receiving any sudden check, as, if the heat be not kept up regularly, the plants are very liable to stop growing, and, when the heat is renewed, to shoot a second time, and thus to waste their strength in sickly and imperfect growth. Great care is also required in autumn to increase the fire heat in proportion as the weather grows cold, so as to prevent the plants from receiving any check from the decrease of temperature in the atmospheric air, as tropical plants may be said to have only two seasons, viz. summer and winter; and thus they should be kept as nearly as possible at the same heat as long as they are in a growing state; and then have a complete change to a season of rest, by never letting the heat rise higher than from 60° to 65° during the dark days of winter. During the winter months very little air can be admitted, on account of the great difference between the air of the atmosphere and that within the house; but in the spring, advantage should be taken of every warm day, even in March and April, to open the sashes a few inches wide for half an hour or an hour in the middle of the day, when the sun shines; but the house should be shut up immediately if the sun should go in and the air become chilled. As the summer advances, air should be admitted freely, and continued till the beginning of September, when it should be gradually reduced till the cold of winter prevents any being given at all. Most gardeners repot, or shift, as they call it, all their bark-stove plants about the middle or end of April; but this is too indiscriminate a practice, and, therefore, only those should be repotted that appear to want such an operation.

One of the greatest difficulties attending the culture of plants in a bark stove is, guarding against the ravages of the immense number of insects that are engendered by the heat; and one of the most troublesome of these is the active little mite called by gardeners the red spider (_Àcarus telùrius_). This little pest breeds in the bark, and when first hatched it is so small as to be scarcely perceptible; particularly as it is of a pale green, nearly the colour of the under side of the leaf, to which it fixes itself, and there spins a web. As it gets older it becomes of a brownish red, and having eight legs, it runs with the greatest rapidity. It is also furnished with a proboscis, with which it sucks the juices of the leaves, making them wither and shrivel up; and thus the flowers and the fruit of the trees are both spoiled, as neither can attain perfection unless the sap that is to nourish them be first properly matured in the leaves. Tobacco smoke, and most of the other usual remedies against insects, have no effect on the red spider; and, though sprinkling it with very cold water will kill it, it is difficult to apply without injuring the plants. The best remedy is allowing plenty of air to pass through the house, whenever the weather is hot enough to allow the atmospheric air to be admitted with safety.

The culture of the plants contained in the _dry stove_ requires considerable care. The Cáctus family may be arranged in three groups; first, the Tree Cacti, which are included in the genus Cèreus, and have long slender stems without a single leaf, sometimes thirty or forty feet high, and not thicker than a man's arm. These plants grow on the summits of the mountains in Brazil, and only require greenhouse heat in England. Secondly, the Mammillàriæ and Echinocácti, which grow in the valleys of the temperate parts of South America, and should be kept in a warm greenhouse in this country; and thirdly, the Melocácti, the Epiphýllum, the Opúntiæ, and the Rhípsalis, which grow in the tropics, and require a dry stove in England. These plants should be grown in pots well drained with cinders, and they should be kept almost without water from October till March, and then watered profusely till they are about flowering, when the quantity of water given to them should be gradually diminished. Some cultivators keep a few of their plants in a bark stove, and plunge the pots in the tan, and they are said to thrive on this treatment, if carefully managed; but as it requires a great deal of care to prevent them from damping off, the ordinary way is the safest for an inexperienced gardener. Mesembryanthemums, which are also kept in a dry stove, require the same treatment as the Cácti.

The orchidaceous plants grown in a _damp stove_ are all epiphytes, which, in their natural state, grow either on the branches of trees, or on exposed rocks. The former of these are found in their wild state with their roots hanging down in the air, and growing in dense forests, where shade, moisture, and excessive heat are essential to their existence. Most of these plants, in a state of culture, are grown in the husks of cocoa-nuts, half filled with moss, from which the roots hang down, or they are tied with wire to pieces of wood hung from the rafters. The wood generally preferred for this purpose in England is the robinia, or false acacia, on account of the roughness of its bark, and the softness of its wood: and moss is generally put between the epiphyte and log so as to make it quite compact. Some genera of orchideous plants, such as Dendròbium, Epidéndrum, and Cattlèya, are always grown in pots, which are filled with turfy peat, chopped moss, and lime rubbish. Others, such as Stanhòpea and Catasètum, should be grown in baskets half filled with moss, or in a curious kind of frame, made of pieces of turf fastened between four upright pegs of wood; as the flowers of these plants come from their roots, and they must be allowed abundance of room to enable them to protrude properly. The baskets or frames for the Stanhòpea and other root-flowering plants should be from three to six inches deep, and from six to ten inches wide; and the frames should be filled with strips of turf, two or three inches wide, piled up on one another so as to fill the frame, and yet leave a sufficient space between to admit the passage of the flower stems which protrude downwards from the root. When orchideous plants are grown in pots, the pots are drained with cinders, and then filled with chopped turf mixed with lime rubbish to keep it open. The exotic ferns grown in the same house require no particular care, except that of potting them so as to insure perfect drainage, and keeping them frequently syringed overhead.

There may be said to be five kinds of greenhouse; viz., the Australian house, the common greenhouse, the heath house, the conservatory, and the orangery, to which is sometimes added, the camellia house, though these plants are generally kept in the conservatory.

The _Australian house_ contains all the curious New Holland plants, such as Bánksia, Dryándra, Grevíllea, Melaleùca, Callistèmon, Metrosidèros, and various genera belonging to the Leguminòsæ, together with the Cape plants belonging to the Proteàceæ and Compósitæ. These plants require a considerable degree of heat, and also as much air and light as can be given to any plants which require shelter from the open air. On this account they are generally grown in curvilinear houses, that is, houses that have glass on all sides, like that in the garden of the London Horticultural Society at Turnham Green. All the plants contained in this house are extremely difficult to grow, and they require the greatest care in watering, so that they may never have too much, and yet never be suffered to become too dry. Houses of this kind are generally heated by pipes of hot water, and kept at a temperature of from 40° to 50° or 60°. There is no pit in the centre, and the plants are either planted in the ground as in a conservatory, or kept on a stage formed of wooden shelves.

The _common greenhouse_ has a brick wall at the back, with a glass roof at an angle of about 45°, and upright glass at the front and sides. The plants are grown in pots placed on a stage or range of wooden shelves rising one above another, with a path all round, and a shelf for the plants under the glass in front. All the sashes are made to open, as it is essential that there should be a free circulation of air; and so little fire is necessary, that one fireplace will be sufficient to heat a greenhouse from thirty to forty feet long, and from twelve to fifteen feet wide. The house may be heated either by hot-water pipes or by flues; in the latter case the flue should go round at the front and return at the back, being about twenty inches high and twelve inches wide. The heat of a greenhouse of this nature need never be more than 50° in the day, and it may be allowed to sink even as low as 35° at night, the object being merely to keep out the frost.

The _heath house_, like the Australian house, requires to be as transparent, and as thoroughly ventilated, as possible. A heathery, however, is generally a span-roofed house with a walk down the centre, and shelves for the plants on each side. It is usually heated by hot water, the pipes for conveying which are placed in the centre of the house. The width of the house should be about ten feet, and the height in the centre of the span should never exceed nine, as it is of great importance to have the plants as near the glass as possible. The floor of the house should stand one foot above the level of the ground: and, where expense is not an object, the house is sometimes built on arches to insure perfect dryness. All the windows are made to move in every possible direction so as to admit of a current of air through the house, whenever the state of the atmosphere will permit it.

The _conservatory_ has all the plants growing in the soil, instead of being in pots and placed on shelves. It is generally more lofty and architectural than a greenhouse, and of much greater extent; and it is frequently attached to the house, being so contrived that it can be entered from one of the living-rooms. The temperature of the conservatory is generally rather warmer than that of the common greenhouse, as it is kept at 60° during the day, and seldom allowed to fall lower than 40° at night.

The _orangery_ is a still more architectural-looking building than the conservatory, and it has an opaque roof. It is used only for preserving orange trees and other plants that remain in a dormant state during the winter, and it requires no more heat than is absolutely essential to keep out the frost.

The _camellia house_ is generally formed like a common greenhouse, but so contrived as to allow the whole of the sashes to be taken off during the summer. The plants are kept on stone shelves, raised one above another; and there is generally no walk at the back.

Of the culture of the plants in the Australian house I have already spoken; and of those in the greenhouse I need only detail the management during the winter months, as your greenhouse will, I suppose, be in the reserve-ground, and will be only used to preserve those plants during winter which you have kept in other more conspicuous situations during the summer.

Many persons injure greenhouse plants by keeping them too warm, and giving them too little air during winter, and then are surprised that their plants become sickly and remain without flowering, notwithstanding all the care and expense that have been bestowed upon them. No greenhouse ought to be kept at a greater heat at night than from 35° to 40°; and in the daytime it should not be allowed to rise above 50°, or at most 52°. When there happens to be sunshine, the fire ought to be lessened, and whenever the air is not frosty the windows ought to be opened from twelve till two every day. If a greenhouse is kept too warm, it will induce premature vegetation, and the plants will waste their strength in an attempt to produce flowers and fruit, at a season when nature requires them to be kept in a state of complete repose. Greenhouse plants should be watered generally every morning; but in frosty weather water need not be given every day, and some plants will not require watering oftener than once a week. This, however, must depend in a great measure on circumstances, and, as a general rule, it may be observed, that water may always be given in small quantities when the surface of the earth contained in the pot looks dry. The pots should never be allowed to stand in saucers, as stagnant water is peculiarly injurious in winter. Whenever the earth looks black and sodden, the plant should be turned out of the pot, and, after the black earth has been carefully shaken from the root, it should be repotted in fresh soil, an inch or more in the bottom of the pot being filled in with small pieces of broken crocks.

In February or March greenhouse plants should be looked over, and repotted where necessary; those that are too tall should be cut in, and cuttings made of their shoots. The young plants raised from cuttings made in autumn should be repotted in larger pots for flowering; and where the plants do not require fresh potting, but have the surface of their mould become green and mossy, the moss should be taken off, and the ground slightly stirred with a flat stick, taking care, however, not to go so deep as to injure the roots. When trouble is not an object, all greenhouse plants are the better for repotting once a year, either in spring or autumn; and when the ball is taken out of the pot for this purpose, it should be carefully examined, and all the decayed parts of the roots should be cut off. Sometimes, when the ball of earth is turned out, nearly half of it will fall off almost without touching it; and when this is the case, it will generally be found that there is a worm in the pot. Worms do a great deal of mischief to greenhouse plants in cutting through the roots, as their instinct teaches them to make their way through the earth straight across the pot and back again, and they cannot do this without tearing the roots asunder every time they pass.

Another point to be attended to in the management of a greenhouse is, keeping the plants as near as possible to the glass, as, unless this be done, the plants will become what gardeners call "drawn up," that is, they will be unnaturally tall and slender, from the efforts they make to reach the light.

As I have frequently mentioned _repotting_, I may as well tell you here the best mode of performing the operation. The pot to which the plant is to be removed should always have been previously washed quite clean, and be perfectly dry. Some bits of broken pots, called potsherds, should then be put at the bottom of the pot, the quantity varying from three or four pieces (so as just to cover the hole) to a mass an inch in depth, depending upon the nature of the plant. If the plant has not been in a pot before, the roots are then placed just above the potsherds, and the earth is filled in, the plant being occasionally shaken so as to allow the earth to get amongst its roots. The soil is next consolidated by shaking the pot, and then lifting it up and setting it down again with a jerk; and is rendered firm and neat round the rim by means of a broad smooth piece of stick shaped somewhat like a table-knife, and called a potting-stick. When a plant has been in a pot before, and is repotted or shifted, as it is called, into a pot a size larger, the plant is turned out of its old pot by putting the hand upon the earth and turning the pot upside down; or, if the ball of earth does not come out readily, striking the rim of the pot against the edge of the potting-table or shelf. The ball containing the plant will thus drop out into the left hand; and the potsherds that adhere to the bottom of the ball having been picked off, and any part of the root that appears decayed having been removed, a little mould is put on the drainage in the new pot; and the ball of earth, containing the plant having been placed in the centre, the space between it and the pot is filled in with light rich mould, and made firm with the potting-stick. The operation is concluded by shaking the pot, and then taking hold of the rim with both hands, and striking the bottom of the pot two or three times with a jerk against the potting-bench. The plant is then watered, and set in the shade for the remainder of the day.

_Heaths_ are very difficult plants to manage; but a great improvement has taken place in their culture within the last few years. They are grown in what is called heath mould, that is, a mixture of peat and sand; and when this earth is put into the pot, it is mixed with good-sized entire pebbles, some of which are suffered to protrude through the surface of the soil. The roots of heaths are extremely fine and hair-like, and the shelter afforded by the pebbles is so congenial to them, that, if one of the stones be taken out, a cluster of fine, white, vigorous roots will be found below it. The plants are always potted high, so as to let the base of the stem be above the level of the rim of the pot, as the plants are very apt to damp off if the collar of the plant be buried in the ground. Heaths should never be suffered to become too dry, and never kept too wet. They require very little heat; and many experienced cultivators never apply fire-heat to their heatheries at all, but merely keep out the frost by having wooden shutters to the sashes, and covering them with mats. Heaths, when growing rapidly, should be repotted whenever the roots have filled the pot; but they should not be shifted too often; and, when they have attained their full growth, they may be suffered to remain in the same pots three or four years without injury.

As plants in the _conservatory_ are grown in the free soil, they are in a much more natural state than any plants can be in pots, and consequently they require much less care in their culture. There is usually a walk all round the conservatory, next the glass, and one down the middle, on each side of which are the beds containing the plants, and under which are placed the hot-water pipes that warm the house. The consequence of this arrangement is, that the beds on each side the middle walk are so planted as to have their highest shrubs in the centre, shelving down to those of lower growth on each side; and hence the centre is generally planted with tall camellias, acacias, metrosideros, eucalyptus, &c.; while near the walk are placed oleanders, myrtles, fuchsias of different kinds, together with chorozemas, and many of the other most ornamental New Holland plants; and up the pillars that support the roof are trained kennedyas, bignonias, ipomœas, and passion-flowers in great variety. Cliánthus puníceus and Polýgala oppositifòlia ought to find a place in every conservatory; and a plant of Wistària sinénsis may be trained under the rafters so as to afford shade to the camellias; as, under shelter, the wistaria will flower twice in the year, and its flowers will yield a delightful, though very delicate, fragrance.

As it is of the greatest importance to the health of the plants to have the soil in a conservatory well drained, many persons form the beds by excavating pits of the proper size, about two feet and a half deep, and put at the bottom a layer of brick-bats, stones, and other materials for drainage, about six inches thick. On this is deposited a thin layer of coarse rough gravel; and on the gravel a layer of rich mould, which should be about two feet thick in the centre of the bed, where the largest shrubs are to be planted, and shelving off to about sixteen or eighteen inches at the sides next the walks. All the sashes should be made to open, and there ought to be large glass doors in front, which should generally stand open during the day in summer, in order to admit as much air as possible.

In some places a movable frame is contrived for a conservatory, into which sashes fit in winter, and which, in severe weather, is covered with tarpauling, made to pull down, like a blind, from a roller along the ridge of the roof; the whole frame being so contrived as to be entirely removed in summer. The upright posts of this frame are let into holes in the ground, like the posts in a drying-ground, so that when the posts are taken out, the holes may be stopped up with wooden plugs with rings attached; and the roof and horizontal pieces fit into each other, and into the uprights, the whole being kept firm by bolts. When a conservatory of this kind is to be removed for the summer, the side sashes and doors are taken away first, generally about the middle or end of April. A week or ten days after, the sashes of the roof are taken off, but the frame and tarpauling are left in case of spring frosts; and, when all danger from these is over, the whole of the framework is removed, and the orange trees, camellias, and other exotic trees that have been planted in the conservatory, appear to be growing in the open air.

The _orangery_ is often contrived so as to be used as a kind of living-room during summer, as it is only intended for the reception of the orange trees, and other plants belonging to the genus Citrus, during winter. The trees are generally grown in large tubs and boxes, in a rich loamy soil, and are set out in the open air during summer, when they require but little care, provided they are frequently watered over the leaves, though they do not like much water to their roots. When young plants are raised from seed, they seldom flower till they have been budded or grafted from an old tree. Orange trees are generally put in the open air in May, and kept there till September or October; and they are very seldom shifted. They require scarcely any light or water during winter, and no heat beyond what is necessary to protect them from the frost.

Some of the varieties of Caméllia japónica are sufficiently hardy to grow in the open air in the neighbourhood of London, provided their roots and the lower part of their stems are mulched; that is, covered with straw or litter, and the main trunk wrapped round with a hay-band a few inches from the ground. The hardiest kind is the variegated red. Camellias seldom do well in pots, except when they are very small, as, when they attain a tolerable size, the flower-buds are very apt to fall off without expanding. The best mode of growing camellias is, therefore, to plant them in the free soil of a conservatory, taking care that some creeping plant is trained along the rafters over their heads, as they do not like to be exposed to too much sun, unless they have also a great deal of air, and are frequently and regularly watered. The soil for camellias should be peat mixed with a little sandy loam. The temperature of the camellia house should be from 50° to 60° during the whole of the growing season; but, when the flower-buds have formed, the glasses are generally taken off during the rest of the summer. Early in autumn, however, when the flower-buds begin to swell, the glasses should be put on and the house kept warm, the plants being regularly watered morning and evening, as, if the watering be neglected a single day, or if stagnant water be suffered to remain about the roots, the flower-buds will be sure to drop off without expanding. Camellias do not require frequent repotting. Small camellias are generally shifted only once in two years, and large ones, that is, those above five feet high, not oftener than once in three or four years. The time for shifting camellias is just when they have done flowering, before they are beginning to send out their young shoots. Great care must be taken when they are repotted not to bruise the roots, as they are very easily injured.

Both camellias and orange trees are very subject to the attacks of the _black fly_, a kind of aphis. The best way of destroying these insects is to syringe the plants well, laying them down on their sides when they are in pots, or, if they are planted in the free soil, syringing them with a garden engine so as to throw the water in a powerful stream upwards, in order to get at the under surface of the leaves, where the insects are generally found. Some persons recommend fumigating with tobacco smoke; but I have never found it so efficacious as syringing, and washing the under surface of the leaves with a sponge, in case the insects should be very numerous.