# Midland Naturalist/Volume 01/Raphides and Plant Crystals

Raphides and Plant Crystals.
By Mrs. G. R. Cowen.
Deposits of mineral matter in a crystalline form are frequently found in vegetable cells, where they are at once brought into view by the use of polarised light. They are commonly termed Raphides, or needle-shaped bodies, a term inappropriate to many of them, in which the crystals are of different forms, often prismatic or stellate,
As early as Malpighi's time, Raphides had been observed in plants, and at later periods they engaged the attention of Quekett, Lindley, Schleiden, and others, but they appear to have looked upon them as products of disease, or an accidental circumstance in the economy of the plant. The first to reduce to something like order, and to indicate the value of plant crystals, both as a constant and intrinsic result of the healthy life of certain plants, and also in determining the differences between species, was Professor George Gulliver, by whom they have been arranged in three groups, viz: Raphides, Sphæraphides, and Crystal prisms.
The crystals are mostly composed of oxalate of lime, sometimes with magnesia. In other instances the calcareous base is combined with tartaric, citric, or malic acid, and the acicular crystals usually consist of phosphate of lime.
Raphides are slender, needle-shaped crystals, with rounded smooth shafts vanishing at each end to a point. About ten to fifty or more lie parallel together, so as to form a bundle which partially fills a cell, or intercellular space. When undisturbed, this brindle lies along its cell, but the Raphides are so easily displaced by slight pressure that either all or part of them cross the cell in various directions, sometimes escaping from the ends. The raphis-cell is commonly very distinct, often oval, and contains some viscid, semi-fluid substance. in the midst of which lies the bundle of Raphides. The raphis-bearing plants among our native exogens belong to three orders, Galiaceæ, Balsaminaceæ, and Onagraceæ, and there is not a single instance of any species belonging to these orders without Raphides.
The Fuchsia belongs to the order Onagraceæ, and is a great raphis-bearing plant, quantities being found in the leaves, the berry-pulp, ​and even in the ovule. In this order, even the seed-leaves, fragments of stem, as well as parts still alive underground during the winter, may be easily known by their Raphides from planta of other and closely allied orders.
None of our exogenous trees or shrubs have, up to the present time, been found to produce Raphides, but they are present in many exotic trees and shrubs of this class. In the order Vitaceæ, of which the grape vine and American creeper are common representatives, we find both Raphides and Sphæraphides in the leaves, young shoots, ovaries, and ripe fruit. Our dictyogens abound in Raphides, as may be seen in the Black Bryony and Herb Paris. In the former they appear loose and destitute of a cell, both in the ripe berry-pulp, and the root stack. This root is like a little yam, and the yams so commonly used as food in the West Indies belong to this class, and contain Raphides.
The sarsaparilla of the shops affords Raphides, but not so the American or false sarsaparilla, which is one of the Araliaceæ, abounding in Sphæraphides.
In the other classes of our endogens, Raphides are more abundant than in our exogens. They are plentiful in the Hyacinth, the Star of Bethlehem, the Cuckoo-pint; also in the Lily of the Valley, the Asparagus, and in the Daffodil and other Amaryllids. We find them plentifully in most species of Duckweed, without the protection of a proper cell wall, the boundary of the space being formed merely by the outer walls of the contiguous tissue-cells. Raphides also occur in the English Orchidaceæ. They vary in length from 1-27th of an inch to 1-500th of an inch.
Sphærayfhides are more or less rounded forms, made up of a number of crystals, commonly opaque and whitish. They are generally rough on the surface, from the projections there of the crystalline angles. They vary very much in size in the same plant, and still more in different orders, and are universally diffused through Phanerogamia. Some plants of the Cactus tribe, when aged, have their tissues so loaded with them as to became quite brittle. The leaves or stem of the Hop, Nettle, and many Goose-foot weeds, are good plants for Sphæraphides; and so are the Begonias of our greenhouses. They are very large in the Prickly Pear.
Crystal prisms are also acicular forms, but seldom occur more than two, three, or four in contact, and then closely side by side, as if partially fused together. They are more frequently strewed singly throughout the plant tissue, and sometimes, as in the bulb-scales of Shallot, they form crosses. They are generally larger than the Raphides, and can be plainly seen to possess three or four faces or angles; they do not taper at the ends like the Raphides, but their tips are either pyramids, or like a carpenter's chisel, or wedge-shaped, or the ends may be truncate, an appearance often caused by fracture. These crystals, when they lie in contact, are not easily separable from each other, or from the tissue in which they are seated, and when the cell can be seen it is closely ​investing the prism. In size they vary from 1-25th inch, and thickness of 1-532nd inch, in the Florentine Iris, to a length of 1-1000th inch, and thickness of 1-6100th inch in the ovary coat of Centaurea nigra.
These prisms are small but distinct in the ovary coat of many Composite, as the Thistle, Knapweed, &c., but large ones occur in many exotic exogens, of which examples may be seen in the barks of Quillaya and Guaiacum. They are frequent in endogens as in the common purple Flag, and many other Iridaceæ, and often appear in the same plant with Raphides, as may be seen in certain Amaryllids; they can be well seen with polarised light.
Although the precise use of these crystals in the vegetable economy is obscure, we may conclude that whatever is constant in a plant must be important. And when we consider how commonly plant crystals are composed of phosphate or oxalate of lime, or same other compound of this earth, and its value in the growth or nutrition of animals and vegetables; and that they are plentiful in many plants which form the food of birds and mammalia, and food and medicine for man, we get a glimpse of the use of these crystals. Raphides are useful in systematic botany in distinguishing between species. We can also easily see why the gardener collects decayed leaves for his composts, and why such plants as abound most in crystals are the most valuable for the purpose. The above account has been compiled from various articles by Professor Gulliver, in the "Microscopical Journal," "The Annals of Natural History," and other scientific journals.
This work was published before January 1, 1930, and is in the public domain worldwide because the author died at least 100 years ago.
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