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over the other, the cisterns must be narrower, and of course more are required; indeed, in this case, trough-pipes would probably be found most convenient.

In orchideous houses and plant stoves, slate cisterns placed above the pipes may be advantageously employed to increase the moisture, but they never reach the temperature of the zinc cisterns, seldom exceeding 80° or 85°; they require, therefore, to be larger, and more numerous. Such cisterns are admirably adapted for water plants; and a range of them extending along the whole front of a hot-house instead of shelves, would be a most useful as well as ornamental addition.

Having pointed out what I conceive to be the best method of supplying moisture to the atmosphere, it remains that I should say a few words on other methods of attaining the same object ; and first of steaming, an operation which at present seems to be greatly in vogue.

By steaming, I mean the discharging into the atmosphere of a house, in large quantities, the steam of water heated to boiling in a close vessel ; it is difficult to conceive how an operation so exceedingly unnatural should ever have been devised, except from a conviction of the extreme necessity of moisture, and the inadequacy of all the ordinary means employed to provide it. The device proved, at least, that gardeners began to be conscious of the unnatural dryness of the atmosphere of their houses, and anxious for any expedient, however unnatural, to counteract it; and, considering the state of many plant houses, it is not surprising that its effects, as occasionally employed, should, for a while at least, be apparently beneficial. . Food, though scalding hot and rather unwholesome, is better than absolute starvation to plants as well as men; but, nevertheless, it is my firm conviction, that steam is invariably injurious in a greater or less degree, and will speedily be found so, even by those who at first have had every reason to be satisfied with its effects. I have repeatedly tried it myself, under divers modifications, and have never failed, sooner or later, to perceive its most injurious effects. Indeed, its injuries are for the most part not long in manifesting themselves. The only case in which it is not evidently injurious is in large houses, where the volume of air is great, and the steam is converted into vapour long before it reaches the plants. For it must ever be borne in mind, that steam from close boilers, and vapour from water heated in open vessels, are essentially different things. Both are alike liquids, and both aeriform, and there the resemblance ends. Caloric in a sixfold proportion has entered into the composition of steam, in the form of latent heat, which is discharged among the plants, when the steam is reconverted into vapour, The only modification under which I can recommend this

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steaming process is the following, and it is admissible only because steam is no longer employed. A shallow cistern, about 6 in. deep, and carrying at least 4 square feet of area, with a false bottom of wire or pierced zinc about 1 in. from the real bottom, being provided, the steam pipe from the boiler should be introduced, so as to discharge itself between the real and false bottom; the cistern should now be filled with water nearly to its brim, and the steam laid on. The water will soon be raised to a pretty considerable temperature, and yield an abundant supply of innocuous vapour. This operation may be continued at pleasure, the cistern being filled up as it wastes. Of course, the size of the cistern must be regulated by the size of the house, and my experience is not sufficient to enable me to say what is desirable, but certainly less than 4 square feet would be useless in an ordinary hot-house, say 25 ft. by 13 ft. 6 in.

I may, perhaps, be charged with inconsistency in providing a steaming apparatus to the conical boilers, holding, as I do, such opinions concerning the use of steam. But, under the modification above described, I can conceive some advantage may be derived from its employment; and I believe it has a tendency to destroy insects : moreover, I think it possible that Mr. Beaton's suggestion of employing steam impregnated with tobacco or sulphur might be found advantageous; so that I was willing to afford those who are favourable to such experiments the means of making them. I have a steam pipe to my own boiler, and used occasionally to employ it in the above manner, but often perceived harm, and certainly never could discover any good effect from it; and now having adopted the use of the cisterns above described, I obtain a far more copious moisture than I could procure by any quantity of steam, which should not absolutely boil my plants. This moisture is produced just when I want it, without trouble. During the summer season, the portable steaming apparatus suggested by Mr. Beaton might be found useful, but always under the form above suggested; and, even in this case, I believe that a good sprinkling of water over the floor and flues, hot from the heat of the day, would produce the same effect much more safely. In orchideous houses one is seldom without fire even in summer.

The effect of the zinc cisterns is most satisfactory and natural. At the present season (April 30.), there is a constant fire in my orchideous pit, and of course a copious evaporation from the cisterns. On going into it late in the evening, the plants are found all reeking with an almost tropical dew, and every pore may drink in abundance. In the morning, as the sun's beams begin to raise the temperature, this dew disappears; and, air being

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given as the day advances, the atmosphere assimilates itself in some degree to that of a tropical day; the dew point being 5° or 6° below the temperature. At night the same dew recurs, sprinkling is rendered unnecessary, and the fine rootlets, which bristle into the atmosphere like the spines of a hedgehog, preserve their extremities in full health and absorbing power. Indeed the bulbs of my older stanhopeas are buried in their own rootlets, like the birdsnest-looking masses of imported plants. I believe it impossible to provide an atmosphere more congenial to them.

There is only one inconvenience which arises from any method of moistening the atmosphere, and which of course increases in proportion to the degree of moisture produced, viz. a drip from the glass, which is often fatal to Orchídeæ, and injures the leaves of all plants. At one time this caused me much annoyance. By the following expedient I have rendered it a most valuable auxiliary, and should be much at a loss without it. The bars of my lights being made as smooth as possible, I fix at intervals, say from 15 in. to 18 in., all down them, small pieces of cobbler's wax (putty would do as well, but is less easily removed), which cause the drip to fall wherever I please; and by thus subdividing a bar into small spaces, no one drip is excessive. But this is not all. Many of my plants are suspended on brass rods or chains, fixed from rafter to rafter, under the lights: the dripping points are arranged with reference to these, so that each plant receives a small but constant supply of moisture, which is not allowed to fall on the shoots themselves, but is generally received by a bit of tile, or a little patch of sand,

It remains that I should notice the defects of the cisterns generally employed in hot-houses, especially those intended for Orchideæ. Many of my friends, to whom I have recommended the use of large cisterns, have replied that such cisterns have been repeatedly tried without any good effect; and certainly I have seen large and expensive cisterns in many hot-houses from which no benefit could possibly be derived ; they are generally constructed in the middle of the house in place of a pit, and are mostly of stone or cement. Now, for a cistern to be of any use, it is essential that the water should be at least 5° hotter than the mean temperature of the house; whereas the cisterns alluded to are always from 5° to 10° lower than that mean. They are formed of non-conducting materials, placed generally lower than the flues or heating pipes, and from time to time filled up with cold water, which warms very gradually; whereas, to answer any purpose, the cistern should be formed of good conducting materials, and its bottom be placed higher than the flues or heating pipes. Slate is the only material well adapted for such a purpose; a cistern built in cement, over flues or pipes, would be always liable to leak, and, even if it did not thus fail, the Alues would be inaccessible when repair is necessary. These difficulties probably deterred persons from forming cisterns in the only position in which they can be useful. Those generally employed are nearly useless except as reservoirs of water, and even for this purpose their low conducting power makes them undesirable, as the water in them is always too cold to use with advantage.

In slate cisterns such as now suggested, the much neglected tribe of stove aquatics might find a congenial habitat, and adorn our stoves. Their culture has been neglected principally I believe, because they will not flower without abundant bottom heat. They require a temperature of 75° at the least, and will bear much more ; about 85° is most congenial to them : such a temperature in ordinary stoves it is difficult to give them, for they require to be close to the light, and the bark-bed, the only means of affording bottom heat, in most cases is too far from the glass. In cisterns, placed on the pipes in front of a pit, I have had them in great beauty; Nymphæ'a cærulea with three or four flowers at once, each 6 in. in diameter, and continuing for months in succession : so soon, however, as bottom heat was discontinued, the flowers came few and unfrequent, and dwindled down to the ordinary size of those seen in our stoves.

In conclusion, for all hot-houses, whether fruiting houses or plant stoves, but especially orchideous houses, I recommend zinc cisterns on the pipes, as above described. In plant stoves I should certainly employ some slate cisterns; but, to produce the copious dews I describe, the zinc cisterns are necessary, and quite supersede the use of steam. To those, however, who may still adhere to the use of steam, I should suggest the adoption of the contrivance above described, to be employed either with a pipe from any existing boiler, or with a portable boiler constructed on purpose. The conical boiler would be very compact for this service, but it must be made of copper, or it would be most cumbrously heavy.

The foregoing observations have been thrown out rather with the view of directing attention to the subject, and assisting others to make more accurate experiments and calculations, than with any pretensions to philosophical accuracy. I have endeavoured

I to show that the hygrometric defects of our artificial climates may be pretty accurately estimated, and easily overcome ; defects will doubtless still remain. The perfection of nature, and the innumerable compensating devices of Providence, are not to be perfectly imitated by human art; nevertheless, we may make a much nearer approximation to them than we have heretofore done.

Sevenoaks, April, 1840.

Art. II. On the singular Origin of the Purple Laburnum, and on

the new Field which it opens to the Horticulturist for the Production of Hybrid Plants. By the Hon. and Rev. W. HERBERT, D.C.L. F.H.S. &c.

I Am much obliged to you for the opportunity you have given me of reading M. Poiteau's interesting account of the origin of the purple laburnum, or Cytisus Adàmi, which I had understood to be an accidental hybrid produced in the garden of M. Adam, but which is stated, and (I doubt not) correctly, to have originated from a graft of C. purpureus, of which the bud had perished. I am not aware what the hypothesis of M. Prevost and M. Leclerc, to which M. Poiteau alludes, may be ; but I think I understand how this singular plant must have been produced, and, if I am right in my notion, it opens a field for the horticulturist to produce hybrid plants which perhaps could not be obtained by seed. It is asserted, that, long after the bud on the graft had perished, other small buds formed themselves round it, all of which produced the true C. purpureus, except one, from which proceeded the extraordinary hybrid. I apprehend, that, if attention had been paid to this phenomenon, it would have been found that the bud which produced it was formed exactly at the junction of the bark of the two species, and that the two contributed equally to its formation. A similar effect might perhaps be expected also from a bud formed where the mere bark of the graft is in contact with the wood of the stock. Every bud on a tree is an individual; and, if the graft and the stock from any peculiar circumstances contribute equally to the formation of a new bud, the individuality of that bud may be expected to partake of their joint natures, as much as that of the plant which is raised from hybrid seed. Let it therefore be the object of gardeners who wish to obtain new plants analogous to the C. Adàmi, to kill the bud of the graft after a perfect union has taken place, and to try to force the plant to break again from the seam or edge of the bark that has been inserted. Unless the bud shall be formed on the very seam, or where the bark inserted is thin, so that the bud shall have taken its rise from the contributive powers of the two plants, a new formation cannot be expected.

The circumstances attending the growth of C. Adami are very singular. Upon your tree one branch had reverted nearly to the type of the laburnum, and another nearly to that of C. purpureus, while the central shoots retained the hybrid character; but, on close observation, neither the leaves nor the flowers of the two branches, which had so reverted to the elements of the parents, were precisely similar to them; both however had acquired fertility, while the central shoots continued sterile. From the seed produced on the yellow-flowering branch, several plants

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