preventing it from clogging, and in swelling (for lime in slacking increases greatly in bulk) bulging out the boilers. When the lime is all slacked, the stoppers h h are to be pulled out, and, by touching a trigger, the grates b b fall down, and permit the lime to be raked out at the bottom. One of the two kilns must be always burning, and the lime slacking in the other, that the draught of the former may turn the axis for the latter.

Fig. 83. is another arrangement for the same purpose. Here only one of the two boiler-kilns is shown. The boiler is here a hollow cylinder; the lime is thrown in at the end a, and raked out at b: ccc are the tubes for the affusion of water; d d, the pipes for the circulation of the hot water. The flame from the fireplace, e, passes up through the lime, down on the outside of the boiler, by the flue ƒ; and, finally, up the funnel g: or the boiler may be used as a common one, independent of the lime, by shutting the damper h, and opening two, placed one at each side, as at i, by which the flame passes only on the outside of the boiler. This latter arrangement may be adopted also during the time the lime may be slacking in the internal part of the boiler. The lime is sustained from falling down into the flues, by a grate at k; l is an air tube to burn the smoke of the fuel in the fireplace.

The arguments that may be adduced in favour of this scheme are, that, wherever there is a large range of hothouses, lime is continually wanting for manure, and that thus the lime burnt would be no drug, and the heat disengaged in slacking it might be economically thus employed: that, in the burning of lime, part of the carbonic acid which is disengaged is converted into carbonic oxide, and thus becomes inflammable, and burns; so that the lime itself, in this case, becomes a valuable fuel: that, this being the case, the lime would be burnt with little or no expense; and, instead of the heating of a large range of houses costing a large annual sum, would produce a saving, by yielding a valuable result. The sole argument against it is complication of apparatus: however, experience would soon simplify that greatly.

There are many useful applications of the circulation of hot water yet to be thought of, and many thought of that have not yet been applied. Why might not the feet of outside passengers on night coaches be kept warm by the waste heat of the lanterns? to take one instance out of many.

Should you approve of it [we do most cordially], I will, at a future time, send you some further thoughts on hot water, &c. I am, Sir, yours, &c.

94. Capel Street, Dublin,

April 18. 1833.

ROBERT MALLET.

ART. IV. Rejoinder to the Answer of the Author of the " Domestic Gardener's Manual," on Questions proposed to that Gentleman in Vol. VIII. p. 652. By Mr. J. MAIN.

Sir,

I FEEL very much obliged by your condescension in answering [p. 186.] so fully and so candidly the queries I took the liberty of proposing to you in a former Number of this Magazine. Having given your answer an attentive perusal, I must beg leave to say, that, from the whole of your arguments, it is to me sufficiently obvious that you have not perceived exactly the drift of my questions; your reply relates only to the augmentation of the elements of plants, while my questions referred to the formation of the organisation. This being the case, it is necessary to restate my questions somewhat more fully, and to add some brief comment, which, while it will place the former in a proper light, will also show to what they tended.

My first question is simply this, Can the organic structure of plants be formed by or out of their juices? I call all juices of a plant the sap, whether in its crudest state, as pure water, or after its assimilation into the consistence of resin, gum, oil, milk, pulp, or jelly. In one or other of these conditions it is found in all plants, and either concreted or fluid, occupying the cellular, vascular, or tubular organs, or exuded therefrom, and appearing on the buds, in the flowers and fruit, or on other parts of the exterior. The sap is therefore an important constituent of the system, and quite distinct, in my opinion, from the organic frame which elaborates and contains it. I ask, then, is the latter formed by any possible aggregation of the former? in other words, are the pellicles of the cells, the sides of the vessels, or tubes of the structure, or the fibrous tissues of the various membranes, generated by associations of the rarer or grosser particles, or globules, of the sap? In your various respectable writings, and in your answer before me, you seem convinced affirmatively. This is your position; which (though supported by many great names) I deem untenable, and which, indeed, called forth the queries I presumed to propose to you.

As proof of your opinion as to the organisable properties of the sap, you refer me to one of our first physiological authorities, and to an ingenious experiment made by that acute observer of nature. But as neither the high respectability of the experimentalist nor the result of the experiment itself can bear upon or alter the simple question proposed by me, I must decline giving any opinion thereon, more espe

cially as the results of such experiments are not always uniform, differing according to the time and manner of performance; indeed, I might add, at the will of the performer.

I have already alluded to the sap and membranous frame or structure of vegetables; but there is another equally important matter to be adverted to; I mean, the elements of vegetables. These, you say, are chiefly the constituents of water, viz. oxygen, hydrogen, and carbon; the chemical essences or bodies of which the vegetable frame is compounded; the pabulum by which it is enlarged, and without constant supplies of which a plant remains stunted, or would in the end inevitably perish. All this I firmly believe, and it is an admission which may appear at first sight to be corroborative of all you have advanced, and contend for, relative to the growth of plants; but I presume to think that a little further consideration and explanation will show, not only that such distinction is just, and therefore necessary, in physiological investigations, but that they, viz. vegetable elements and vegetable organisation, should never be confounded together, so as to attribute to the former the power of generating the latter. Your ideas appear to be, that vegetable food, in conjunction with the vital energies and "chemico-electrical influences" of the earth and atmosphere, goes directly to form new organs. My opinion is, that nutrition received into the system goes only to increase the quantity of the elements already existing in the membranous fabric, serving to dilate and expand the same; not by addition of new cells, tubes, or fibres, but simply by enlargement of those already there. You assume that, by certain and peculiar combinations of vegetable elements acted on by "the great natural agents," new organic bodies may be generated. I humbly imagine this to be impossible; because such a phenomenon has never been seen, nor do we ever witness any vegetable body produced, unless it originates from a seed, propago, tuber, or other dissevered member of a plant. The organisation and specific structure are certainly rudimental; these are amplified, as already observed, by the elemental fluids absorbed by the receptive spongioles and pores of the cuticle, but not one additional cell can possibly be formed by any such augmentation of either gaseous or aqueous fluids. Can we suppose, with Buffon, that nature abounds in "living organic particles ;" and that these, by concurring circumstances, associate by accident, and form vesicles, laminæ, tissues, fibres, and all other organic structure, in the same way as crystals are formed? Such doctrine, I presume, cannot be sound philosophy. If there were

not determinate rudimental structure, the combinations of the introsuscepted aliment would be fortuitously arranged, and all specific structure would be irregular and confusedly disposed.

These, my humble opinions of vegetable elements, accretion, and developement, will readily account for my second question, relative to the instances of organic bodies being formed out of inorganic matter, and on which I requested information. On this question you have been pleased to give as an instance the new growth of a potted vine, forced under your own eye. You solicit my attention to the new organisation exhibited in the elongated shoots, and ask whence it came. I feel perfectly confident in stating that the whole was contained in the buds before expansion, and the increase of the elements was derived from the manured earth and water with which the vine was supplied. The chemical elements of carbon, &c., contained in the expansible organisation of the buds were excited into action by heat and light; and, in every moment of the growth, fresh supplies of those elements were received to dilate the pellicle of every cell, elongate every tube, and engross every fibre composing the several membranes of the plant. I could prove by a thousand instances, were it necessary, that vegetable as well as animal organisation has rudimental preexistence. It is a fact admitting not a shadow of doubt; for, if it could be proved that the lowest and most insignificant of vegetables was self-produced, or if even the most inconsiderable portion of a vegetable organ could be formed from the mere union of vegetable elements, then, in the same way, we should not only have adventitious buds, flowers, and fruit, but adventitious herbs, and shrubs, and trees.

Chemistry can form crystals, marble, and even the hardest of all mineral bodies, out of what was once in a state of fluidity; but can any possible combination of chemical bodies and powers originate the smallest Fúngus, or the minutest species of Infusòria? Some natural philosophers labour in vain to account for the primitive formations of plants and animals by their principles of science; and so, I dare think, will vegetable physiologists be puzzled, if they deny preexisting organisation. If, therefore, a plant cannot originate itself, nor acquire existence without a rudiment; so neither, it follows as a corollary, can the smallest member or appendage of a vegetable be developed, unless it arise from a preexisting congenerous membrane. (See Dom. Gard. Man., p. 274.)

From these circumstances we arrive at, I think, a just and rational conclusion, viz., that vegetable sap is not organisable;