cell, which cell is applied closely to the surface, the crystal completely filling it: when muriatic acid is added the crystal is dissolved, and the cell is left visible.

"The most ready method of determining that the acicular crystals are contained within the cells is, to take a piece of the bulb of Scilla maritima and macerate it until it becomes decomposed, or to take some of the rotten portions which are frequently on its exterior; and, by examining either of these with the microscope, it will be seen that there are numbers of isolated cells which contain crystals, which cells are five or six times larger than those of the tissue which have none within them; and, what appears remarkable, the crystals seldom occupy more than a small portion of the cell though it be so dilated, and in the Squill are usually collected at one end, probably by gravitation; but in the biforines they generally completely fill a small portion of the cell, about its middle, the ends containing none whatever.

"To prove the same fact as regards the conglomerate kind, let a piece of the root of Rhubarb, or a part of the frond of Zamia pungens, be boiled till the cohesion of the tissue be destroyed, when some of the separated cells will exhibit one cluster generally in each; but the containing cell is not larger than others of the same plant, and at times very little larger than the mass within it.

"There are some exceptions to Raphides being found constantly in cells, notwithstanding Unger's assertion that they are exclusively found in their interior, and that the vascular bundles have none within them for they can be observed in the interior of the vessels in the stem of the Grape vine; and loose in the anthers, mixed with the pollen, in Hemerocallis purpurea, Anigozanthus flavidus, and many other plants; and they can be observed in the air cavities of and many aquatics.

"The interior of the Stem is the most common situation in the herbaceous plants for Raphides, and it used to be considered the only locality; but the epidermis of the stem of many plants displays thousands, as that of the Tradescantias, Opuntia crassa, others.

"The Bark of many trees also contains them; they are readily observed in the layers of the Lime tree bark, of two kinds: also in the barks of Araucaria imbricata, Cascarilla, Cinchona, and various other plants.

"Even the Pith is not destitute of crystals; for the Grape vine exhibits them in that situation, as does the Lime tree in the medullary rays, which are processes connected with it.

"The Leaves of multitudes of plants contain the various kinds in great abundance; Pisonia, Hemerocallis, and Calla æthiopica furnishing the acicular, whilst Rheum palmatum and undulatum are common examples yielding the conglomerate.

"The Stipules are not without Raphides, for those of the Grape vine show them in situ, but very small in size.

"The Sepals of many Orchidaceæ abound with crystals, as those of Bolbophyllum fuscum and others, and especially the horny labellum of Catasetum.

"The Petals of many plants, like the sepals, contain more or less crystalline matter, which is particularly evident in the small corolla of the Grape vine.

"The Fruit does not so often contain them, yet the common Grape furnishes a sufficient evidence of their existence in that organ.

"In the Root their presence can be easily discovered, especially in all Rhubarbs, varying a little in number from the locality of the specimen; most in Turkish, less in East-Indian, and least in British-grown specimens.

Of

"Number in a Cell. -- The number of Raphides in any cell is subject to much variation. It is seldom that a single crystal is met with; but in the Squill, Calla æthiopica, and other examples, besides the multitude of acicular crystals, some cells which are not dilated occasionally exhibit only one minute rhombohedron, as has been observed by Unger in Papyrus antiquorum. the conglomerate kind, one cluster is the usual number in the respective cells, though in Zamia pungens two such can be at times observed within the same cell. The acicular Raphides are in the greatest numbers, and vary somewhat in quantity in different cells and in different plants; some containing but very few, whilst others contain hundreds.

"Proportion to the Weight of Tissue. The mass of crystalline matter that is formed in the tissue of some plants is prodigious, whilst in others the quantity is very thinly diffused. In several species of Cactaceae the crystals equal if not exceed the weight of dried tissue; this is especially the case in Cereus senilis. In Turkey rhubarb root, one hundred grains yielded between thirtyfive and forty grains of Raphides; and the fact of various rhubarbs giving different feelings of grittiness to the teeth when chewed, is said by Guibourt to be employed as the test of their goodness. In the bulb of Scilla maritima, not more than ten grains are contained in the same weight of dried tissue.

"Size. The acicular vary exceedingly in their measurement, some being not more than Too part of an inch in length, whilst others will be as much as The conglomerate form is not subject to so much variation, varying only from to part of an inch. The size of the rhombohedral and other forms of crystals has no uniformity as to measurement, some being not more than 2, whilst others are the part of an inch.

Composition. According to Raspail, the composition of the acicular and conglomerate forms differs, the former being phosphate, whilst the latter are oxalate of lime. Unger mentions that Buchner, Nees von Esenbeck, and others, have found that their bases are sometimes lime, magnesia, and silica, the latter not often occurring; and that these bases are united to carbonic, oxalic, and phosphoric acids. The whole of these assertions are more or less correct, but Raspail has only given us negative proofs of their composition. It is not difficult to obtain positive ones, by the following experiments :

"If Raphides of the conglomerate form (perfectly free from cellular tissue) be heated red hot, it will be observed that they at first become black and again white, as the heating is continued to redness in this state they readily dissolve in weak nitric or hydrochloric acid, with effervescence; if to this solution oxalate of ammonia be added, a copious white precipitate is obtained, which indicates that the base in this case has been lime. In detecting the acid united with the lime, the proceeding is a little more complicated. For this purpose the crystals are to be dissolved in dilute nitric acid, which occurs without effervescence; to this solution nitrate of silver is to be added, when a heavy white precipitate is produced, which, when washed with distilled water to free it from any excess of acid and nitrate of silver, is to be dried; if after this a small portion be heated in the flame of a lamp it explodes, by which it is proved that the precipitate is oxalate of silver. These results, which may be performed with certainty with conglomerate Raphides, plainly proves their composition to be oxalate of lime.

"The acicular can be demonstrated to be phosphate of lime, by proceeding thus. If heated red hot, they do not dissolve in acids with effervescence, a fact which essentially distinguishes the composition of the two kinds. When dissolved in dilute nitric acid, if oxalate of ammonia be added, we have the characteristic precipitate of lime; if with a portion of the acid solution be mixed a little nitrate of silver, a white precipitate is not obtained, as in the last case, but one of a lemon colour, which is such as denotes the

combination with silver of phosphoric acid, which must have been furnished by the acicular Raphides.

"Though phosphoric and oxalic acids united with lime are found the most frequent components of these minute crystals, there can be no doubt that tartaric acid enters into their formation in certain plants, as in the fruit of the Grape, where the crystals are found of a different figure from those in the interior of the leaves or stem; and also that magnesia can be frequently detected combined with lime, and perhaps never forms crystals with acid, without lime entering also into their composition.

"Silica, though it frequently forms an organised part of vegetables, seldom exists as crystals in their interior. In a bark from Para, which is said to be manufactured into a kind of pottery, silica exists in abundance in granular fragments, which, however, do not put on a crystalline form.

"Conclusion.-It is not known what purposes these bodies fulfil in the economy of plants, but it has been conjectured, since amylaceous matters are deposited, and again appropriated for the support of the carbonaceous portion of the tissue, according to the necessities of the individual, that these crystals may be deposits to be applied towards the mineral part or skeleton of the plant, as occasion may require: but it has been found from experiments that these calcareous bodies are insoluble in vegetable acids, and the silica of course in every thing; consequently they cannot be taken up again, are therefore unsuited to the vital exigencies of the vegetable, and probably are of no use, even mechanically, in the several tissues which contain them, because plants of many kinds do not secrete such formations: therefore, it will be nearer the truth to regard them, as Link has done, as nothing more than accidental deposits.

"In all the analyses lime has been found the greatest constituent of these bodies and since this material is so intimately associated both with animal and vegetable organisation, as not perhaps to be wanting in any individual of either kingdom, there is every reason for its being so generally the base of such crystals. Moreover, since it is the property of some vegetables to combine, out of their materials of sustenance, varied proportions of oxygen and carbon, which, when apportioned in the ratio of three of the former to two of the latter, form oxalic acid, the presence of that agent in a plant, in contact with lime, can scarcely fail in producing a crystalline substance with it. Again, as phosphoric acid is a frequent accompaniment of animal and vegetable organisation either

introduced with the food, or created out of it, (it being yet a problem to solve how this and other elementary matters are produced,) it can be readily conceived why compounds with it and lime should be formed as well as with the former acid; because, as the earthy and other matters are absorbed from the moisture of the soil, they must necessarily meet with these acids when they exist, and the vitality of the plant does not prevent their forming the crystals which have been here described; still there are some curious points connected with their production. If oxalic or phosphoric acid be added to a solution of lime, instead of crystals, a pulverulent opaque precipitate is obtained, which does not happen in the interior of the plants: therefore various experiments have been devised, to discover the method of making crystals by combining the above substances. Some have been ineffectual, such as making a plant, which contains lime in its composition, absorb water with a small quantity of oxalate of ammonia dissolved in it from the want of temperature which would create a necessity for moisture in the plant this experiment failed. A method, however, which succeeded was, to connect a vessel containing a solution of oxalate of ammonia with one containing lime water, by means of a few fibres of cotton: this gradual introduction of one fluid to the other formed perfect crystals of oxalate of lime on the ends of the fibres which were in contact with the lime water. This having succeeded, another attempt was made to form them in the interior of the cells of such plants as did not previously possess them: some difficulty occurred in finding any one fitted for the purpose, and at last Rice-paper, as it is termed, (the concentric slice from the pith of Eschynomene and Hibiscus,) was selected as the best material for the experiment, from its admitting an examination of their formation, by becoming transparent when charged with fluid.

"This substance was placed in lime water under an air pump, and the cells were soon filled with that fluid; it was then dried and submitted two or three times to the same process: by this means the cells were well charged with lime. Portions of this substance were placed in weak solutions of oxalic and phosphoric acids, and allowed to remain. On the third day, when examined, the cells in both instances contained much precipitate, together with numerous crystals; those in the oxalic acid being precisely like the conglomerate form in Rhubarb, and those in the phosphoric being rhombohedra, but none of the acicular shape were found, even after continuing the process beyond eight or ten days.