Sorbus nepalensis. The buds which were subsequently produced were found to be different from those of the scion and of the stock (unfortunately it is not stated what plant furnished the latter) in hardiness, period of leafing, form, &c.; indeed, so different were the new productions, that they were, says M. Carrière, unlike any plant he knew in cultivation. This also may possibly have been a case of variation not necessarily connected with grafting, but it is too singular to be passed over in this place.

Of doubtful origin, also, are the oft-mentioned “trifacial oranges "--oranges in which the fruits presented, blended together in all possible proportions, the characteristics of two or three distinct varieties of orange. As the true nature of these singular fruits is shrouded in mystery, and we can add nothing to their history beyond what is detailed in readily accessible books, such as Lindley's "Theory of Horticulture," or Darwin's "Variations of Animals and Plants," we pass them by here with the mere mention.

The latest development of the graft-hybridisation theory is that according to which certain new or strange variations of the potato have been attributed to this process. The "eyes," or buds, of one kind of potato have been inserted into the tuber of another kind, carefully deprived of its own buds; adhesion has taken place, and new tubers have been formed, differing from those of the parent variety, and producing leaves and haulm also different in character, and to some extent intermediate. It is only right to add, in reference to this point, that the majority of experimenters have failed even in getting adhesion under such circumstances. Others deny the possibility of the occurrence in toto, and attribute any changes that may have occurred to the known variability and tendency to "sport" exhibited by the potato. So far as our own personal experience goes, we have seen several cases of adhesion in potatoes grafted by others; and have ourselves succeeded in obtaining union in one instance. Moreover, there has been abundant evidence to show that some change of an extraordinary character does take place in the new tubers that originate after grafting. Whether or no these changes are due to a commingling of characteristics derived from the stock and the scion is a matter still open to question.

It must not, however, be supposed that all cases of budvariation are due to graft-hybridisation. The evidence in favour of the latter process is as yet by no means free from doubt. Nevertheless, confirmatory facts, or what, so far as we know at present, we have good reason to believe to be such, are gradually accumulating. At any rate, it seems clear that the old notion that graft and scion, scion and graft, have no reciprocal effect, must be given up as untenable.

The physiology of cell life does not at present help us very much in the elucidation of the effects produced by grafting. Those who deny that any effect is produced beyond adhesion of the graft to the stock, and the transmission of fluid from the roots through the latter to the scion, have anatomy in their favour. The tissue below the graft is that of the stock; above it, it is that of the graft-at least under ordinary circumstances. Moreover, it is well known that to a large extent each cell is independent of its neighbour, and often contains very different ingredients, without any intermingling of the contents of adjacent cells. This is well shown in the case of the red beet grafted on the white beet-the two retained perfectly their respective characteristics above and below the union-as well as by other illustrations previously cited. But, on the other hand, this fact should be compared with the transposition of characters presented by the two carrots alluded to in an earlier page. Those who lean to the view that stock does affect scion and scion stock have only exceptional aid from anatomy; but physiologically, they may avail themselves of the circumstance that the passage of fluids, and to some extent the direction of new growth, are now known not to be limited to any single course, but to take place in any direction, according to circumstances.

EXPLANATION OF PLATE LXXI.

a to c, Abutilon.

a. Stock of normally green-leaved Abutilon, on which at b is grafted a scion of the variegated Abutilon Thomsoni.

cc are branches of the stock, the leaves of which have become variegated in consequence of the grafting.

d, e, Roses.

d, a white moss-rose.

e, a red smooth-stemmed Quatre-Saisons rose, proceeding from the same branch as e, possibly as a result of grafting.

155

COAL AS A RESERVOIR OF POWER.

BY ROBERT HUNT, F.R.S.

TH

HE sun, according to the philosophy of the day, is the great storehouse of Force. All the grand natural phenomena are directly dependent upon the influence of energies which are poured forth without intermission from the central star of our system. Under the influences of light, heat, actinism and electricity, plants and animals are produced, live and grow, in all their infinite variety. Those physical powers, or, as they were formerly called, those imponderable elements, have their origin in one or other of those mysterious zones which envelope the orb of day, and become evident to us only when mighty cyclones break them up into dark spots. Is it possible to account for the enormous amount of energy which is constantly being developed in the sun? This question may be answered by saying, that chemical changes of the most intense activity are discovered to be for ever progressing, and that to these changes we owe the development of all the physical powers with which we are acquainted. In our laboratory we establish, by mechanical disturbance, some chemical phenomenon, which becomes evident to our senses by the heat and light which are developed, and we find associated with them the principle which can set up chemical change and promote electrical manifestations. We have produced combustion, say, of a metal, or of a metallic compound, and we have a flame of a colour which belongs especially to the substance which is being consumed. We examine a ray of the light produced by that flame by passing it through a prism, and this analysis informs us that coloured bands, having a fixed angle of refraction, are constant for that especial metal. Beyond this, research acquaints us with the fact that, if the ray of light is made to pass through the vapour of the substance which gives colour to the flame, the lines of the spectrum which were chromatic become dark and colourless. We trap a ray of sunlight and we refract it by means of a spectroscope-an instrument giving

results which are already described in this journal *—when we detect the same lines as those which we have discovered in our artificial flame. We pursue this very interesting discovery, and we find that several metals which give colour to flame, and produce certain lines, when subjected to spectrum analysis, are to be detected in the rays of the sun. Therefore our inference is, that some substances, similar to the terrestrial bodies, with which we are familiar, are actually undergoing a change in the sun, analogous to those changes which we call combustion; and, more than this, we argue that the high probability is, that all solar energies are developed under those conditions of chemical change-that, in fact, the sun is burning, and while solar matter is changing its form, Force is rendered active, and as ray-power passes off into space as light, heat, &c. to do its work upon distant worlds, and these forms of Force are expended in doing the work of development on those worlds. This idea-theoryhypothesis-call it what we may-involves of necessity the waste of energy in the sun, and we must concede the possibility of the blazing sun's gigantic mass becoming eventually a globe of dead ashes, unless we can comprehend some method by which energy can be again restored to the inert matter. Certain it is that the sun has been shining thousands of years, and its influence on this earth we know to have been the production of organised masses, absorbing the radiant energies, in volumes capable of measurement. On this earth for every equivalent of heat developed, a fixed equivalent of matter has changed its form; and so likewise is it with regard to the other forces. On the sun, in like manner, every cubic mile of sunshine represents the change of form of an equivalent of solar matter, and that equivalent of matter is no longer capable of supplying Force, unless by some conditions beyond our grasp at present it takes up again that which it has lost. That something of this kind must take place is certain. The sun is not burning out. After the lapse of thousands of years we have the most incontrovertible evidence that the light of to-day is no less brilliant now, than it was when man walked amidst the groves of Eden. We may venture further back into the arcana of time, and say that the sun of the past summer has shone with splendour equal to the radiant power which myriads of ages ere yet man appeared on this planet stimulated the growth of those luxuriant forests which perished to form those vast beds from which we derive our coal. Not a ray the less is poured out in any hour of sunshine: not a grain weight of matter is lost from the mass of the sun. If either the sunshine was weakened, or the weight of the vast globe diminished, the planets would

* "Popular Science Review," vol. 1, pp. 210-214.

vary in their physical conditions, and their orbits would be changed. There is no evidence that either the one or the other has resulted. Let us see if we can guess at any process by which this stability of the solar system is maintained.

It was first shown by Faraday, in a series of experimental investigations which may be regarded as the most beautiful example of inductive science with which the world has been favoured since Bacon promulgated his new philosophy, that the quantity of electricity contained in a body, was exactly the quantity which was necessary to decompose that body. For example, in a voltaic battery-of zinc and copper-plates-a certain fixed quantity of electricity is eliminated by the oxydation of a portion of the zinc. If, to produce this effect, the oxygen of a given measure of water-say a drop is necessary, the electricity developed will be exactly that which is required to separate the gaseous elements of a drop of water from each other. An equivalent of electricity is developed by the oxydation of an equivalent of zinc, and that electricity is required for the decomposition of an equivalent of water, or the same quantity of electricity would be equal to the power of effecting the recombination of oxygen and hydrogen, into an equivalent of water. The law which has been so perfectly established for electricity is found to be true of the other physical forces. By the combustion-which is a condition of oxydation-of an equivalent of carbon, or of any body susceptible of this change of state, exact volumes of light and heat are liberated. It is theoretically certain that these equivalents of light and heat are exactly the quantities necessary for the formation of the substance from which those energies have been derived. That which takes place in terrestrial phenomena is, it is highly probable, constantly taking place in solar phenomena. Chemical changes, or disturbances analogous to them, of vast energy are constantly progressing in the sun, and thus is maintained that unceasing outpour of sunshine, which gladdens the earth, and illumines all the planets of our system. Every solar ray is a bundle of powerful forces: light, the luminous life-maintaining energy, giving colour to all things; heat, the calorific power which determines the conditions of all terrestrial matter; actinism, peculiarly the force which produces all photographic phenomena; and electricity regulating the magnetic conditions of this globe. Combined in action, these solar radiations carry out the conditions necessary to animal and vegetable organization, in all their varieties, and create out of a chaotic mass forms of beauty rejoicing in life.

To confine our attention to the one subject before us. Every person knows that to grow a tree or a shrub healthfully, it must have plenty of sunshine. In the dark we may force a plant to