would seem to require that the inflammable vapour should be, as it were, prevented from expanding by the vital action, or else that its emission continually renewed, should always keep it dense, around the plant, in proportion as it tended to expand in the external air, two states of things equally difficult to conceive. So singular a fact, however, is known only in a general way among botanists,, without their having observed it themselves, and accurate details of it are to be found only in Deterville's Dictionary of Natural History, where Bosc thus says: "The extremities of the stalks, and the petals of the flowers of the fraxinella, are filled with an immense number of vesicles full of essential oil. On the hot days of summer they diffuse a strong scented vapour, inflammable and so abundant, that if, towards evening when a cooler air rendered it a little denser, we bring a lighted taper near the fraxinella, there appears all on a sudden a great light, which spreads over the entire plant, without injuring it." Chance having afforded me an opportunity of witnessing these phenomena of inflammation of the fraxinella, I determined to study their cause and physical conditions. At first, supposing with those who have described the matter, the reality of an ethereal emanation which encompasses the plant, I instituted, according to this view, different experiments, but none with any success. I then directed my attention to the examination of the cortical vesicles, whence it was said that this inflammable atmosphere emanated. These vesicles, when observed with the microscope, present the form of small bottles, terminated by a sort of conical neck, tapering to a point at its extremity. They have been very accurately described by M. Mirbel in his " Elements of Vegetable Anatomy and Physiology." These are found distributed more or less numerously over every part of the stalk: they are seen in greater abundance on the peduncles of the flowers, principally in their lower surface, at the extremity where the flower is inserted; we may still follow them on the borders of the leaves of the calyx, on the borders and nerves of the petals, and on the stamens and style; in fine, their grains, more condensed, thus cover all the surfaces of the ovaries, when they are enlarged by fecundation. Among these utricles, some are sessile, others pediculated, the latter in different parts, but more frequently on the most vigorous. Very small at the commencement of vegetation, they become enlarged according as

the plant increased. Their surface, seen with a microscope in a strong light, exhibited itself commonly speckled with red and green, in the variety with the red flower; but it is all green in the white flower variety. The interior is filled with a colourless liquid, through which the light is refracted to a focus. I frequently saw at the extremity of this point a small limpid drop, as if a part of the interior liquid, dilated by increase of temperature, or secreted by the vital action, had flown out. These observations lead me to think, that the development of the flame around the plant might be the result of simultaneous inflammation, or almost instantaneously propagated from these numerous utricles filled with essence. On this supposition, the heat of summer was not necessary for the actual production of the phenomenon, but merely for the maturation of the inflammable liquid contained in the utricles; once the utricles were formed and ripened, the cold or heat of the time could not interfere any more than the time of the day. The ignition must be effected merely by the contact of the inflamed body, or at least merely by its contact, in order to make the utricles burst. In fine, it must be accomplished with the characters of suction and propagation suitable to small globules lying in juxtaposition, filled with an inflammable liquid, not with the instantaneous simultaneousness of a volume of gas. This is the mode of viewing the phenomenon, to which I have been led by all the experiments which I have made, some of which I shall here state. On the 26th of April 1830, I tried to apply the flame of a match to the peduncle of a flower of the red variety, which appeared to me already charged with a certain number of utricles considerably distended. I did not obtain continued inflammation, but mere local crepitation, similar to those produced by jets of the essence contained in the orange peel, when pressed and held near the flame of a taper. The remainder of the plant, where the utricles were smaller and fewer, did not present even this phenomenon. I repeated the experiment the following year, and at the same time of the year, with similar results. In the parts where the crepitations were produced, the utricles appeared obliterated and blackened. On the 15th of May 1830, several flower-stalks had acquired full development: the utricles were considerably expanded, and closely set on their surface.

The entire day was cold and dry. In the evening the temperature being at 49° F., I repeated the attempt to inflame. The attempt succeeded when the flame was applied beneath the peduncles of some flowers fully developed, or only partly expanded, particularly near the commencement of these flowers, where the utricles are always more abundant. The inflammation, though manifest, was not sufficient to pass spontaneously from the base of one flower to that of another; it was necessary to excite it at each point in succession, which I did with sufficient gentleness not to injure the stalks. Among those which presented the phenomenon, there were some which I had in vain tried the preceding April; some others, whose utricles having been inflamed were destroyed, might still, after the lapse of a week, be ignited anew, no doubt in consequence of other utricles having come to maturation since the preceding experiment. In the third attempt, on the 22d May, the development of the plant being more advanced, the inflammation was excited with great intensity over all the stalks. I have frequently since produced a repetition of the phenomenon on the same flower-stalk at different periods; and, having become more dexterous in conducting the process, I have been able to reproduce it seven or eight times this year in a sensible degree on the same stalk, by choosing successively its different parts to apply the inflammation to them. It is not necessary that the experiment should be made particularly in the evening any more than at any other time. In fine, the inflammation is always propagated from below upwards, over an entire bunch of flowers, but with much more facility from above downwards: it may also take place on the peduncles of the centre, without occurring on the lateral peduncles, though they may be in a fit state to receive the inflammation, by approximating the flame separately to their surface. This possibility of succession in the phenomenon of ignition, as well as of its insulation, is very easily understood for a system of globules separately distributed over all the parts of the plant; but it cannot exist for a continuous mass of inflammable vapour, such as that with which the fraxinella was supposed to be encompassed The phenomena just described are produced on all the varieties of the fraxinella, whether the red flower or white flower variety, less easily, however, and less abundantly, on the latter, its utricles appearing smaller

and fewer. It is known that external temperature, by modifying the progress of maturation, considerably influences the absolute quantity of essential oil produced by the same vegetable. The cold constitution of this year seems to have thus acted on the phenomenon just described; the utricles of the fraxinella are smaller, and their inflammation appears less abundant, than in the preceding years.-Dub. Journ. of Med. and Chem. Scien. No. viii. p. 29.

11. Influence of Coloured Rays on the Growth of Plants. By M. C. MORREN. In a paper which the author read to the Academy about two years since, he had shewn that, of all the elementary colours, those which are most favourable to the manifestation and development of organized beings, belonging either to the animal or vegetable kingdom, are red and yellow, and that this property exists in a nearly equal degree in each. These, and other experiments, were verified at that time only in the case of the most simple organized beings, in masses of water subjected to the influence of the agents of the surrounding world. M. Morren has tried whether the same results would take place on making coloured rays act separately on earth in which some grains were put to germinate. The experiments were commenced on the 17th of March of this year. He took nine pots filled with well dried earth, and of the same kind for each, and in each pot he sowed twenty grains of cresses (Lepidium sativum). These seeds were then covered with a bed of earth, three millimetres in depth. He sprinked each pot with the same quantity of water from day to day. He covered each with a tin vessel, blackened both inside and outside, twenty-two centimetres in height, of a cylindrical form, one decimetre in diameter, shut superiorly by a plate of tin, placed obliquely, and inclined at an angle of 45°. Each plate was perforated in the centre with a circular hole, before which was placed a circular pane of glass, four centimetres in diameter, and differing in colour for each vessel. These pieces of glass were such as are used in ornamenting the old windows of churches, and were all of the most beautiful tint: they were of the following colours, -violet, blue, grass-green (vert pré), sea-green, bright yellow, yellow, orange, red, purple. By the side of these vessels he placed another vessel, black, such as themselves, but with a white plate of glass. No ray passed through the solder, and care

was taken to sink each vessel one inch and a half in the ground. These were all placed on a shelf, raised to one-half the height of a lightsome window. The fourth day of the experiment the radicles had shot out under all the vessels, and attained the length of from one to two millimetres. The sixth day it was observed that the vegetation was much more advanced under the vessels than in the open air, and under the influence of the compound light. Under the yellow, and particularly under the bright yellow, the radicles were scarcely more developed than on the fourth day. Under the green rays there were some radical hairs towards their upper part, which was somewhat yellow. The small plumulæ were yellow; the radicles and hairs were also as under the yellow rays. The orange, red, purple, blue, and violet rays, corresponded to radicles of a centimetre, yellow in the neck, to radical hairs of a millimetre, to plumulæ frequently curved and well formed. On the seventh day the plumulæ were developed under all the vessels; they were very yellow. Under the white light they were becoming sensibly green; in the open air they appeared green. On the eighth day the shoots were from one to one and a half centimetre in length; under the yellow rays they were not so long, white all over, the plumula yellow, the leaves the same, and bent back, the radical hairs two millimeters in length. Under the white light the shoots were scarcely three millimetres in length; they were becoming green, as also the leaves. On the ninth day there was an identity of character with respect to all the plants under the vessels; shoots of three centimetres, leaves of four millimetres, curved back very much, entirely yellow. In the air, the shoots were scarcely a centimetre in length, the leaves very green. On the fifteenth day of the experiment there was observed, at length, a strange difference with respect to the plants developed under the yellow rays, their leaves were become green, though paler than those plants in the open air. Under the orange rays a slight greenness presented itself. Under all the other rays the plants were evidently suffering, and were yellow. From these researches the author concludes, 1. That, in the same way as darkness favours the first period of germination, so also do the colours of the spectrum, acting separately, possess a specific influence which seconds this operation; but that among these colours, those whose illuminating power (with the exception of green) is great