MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 363 



359. Deposits of Mineral matter in a crystalline condition, known as 

 r aphides, are not unfrequently found in vegetable cells; where they are 

 at once brought into view by the use of Polarized light. Their designa- 

 tion (derived from paq>i$, a needle) is very appropriate to one of the 

 most common states in which these bodies present themselves, that, 

 namely, of bundles of needle-like crystals, lying side-by-side in the cavity 

 of the cell; such bundles are well seen in the cells lying immediately 

 beneath the cuticle of the bulb of the medicinal Squill. It does not apply, 

 however, to other forms which are scarcely less abundant; thus, instead 

 of bundles of minute needles, single large crystals, octohedral or prismatic, 

 are frequently met with; and the prismatic crystals are often aggregated 

 in beautiful stellate groups. One of the most common materials of 

 raphides is Oxalate of Lime, which is generally found in the stellate orm; 

 and no plant yields these stellate raphides so abundantly as the common 

 Rliubarl), the best specimens of the dry medicinal root containing as much 

 as 35 per cent of them. In the cuticle of the bulb of the Onion the 

 same material occurs under the octohedral or the prismatic form. In 

 other instances, the Calcareous base is combined with Tartaric, Citric, or 

 Malic acid; and the acicular raphides are said to consist usually of 

 Phosphate of Lime. Some Eaphides are as long as l-40th of an inch, while 

 others measure no more than l-100th. They occur in all parts of plants, 

 the Wood, Pith, Bark, Root, Leaves, Stipules, Sepals, Petals, Fruits, 

 and even in the Pollen. They are always situated in cells, and not, as 

 some have stated, in intercellular passages; the cell-membrane, however, is 

 often so much thinned away as to be scarcely distinguishable. Certain 

 plants of the Cactus tribe, when aged, have their tissues so loaded with 

 raphides as to become quite brittle; so that when some large specimens of 

 C. senihs, said to be a thousand years old, were sent to Kew Gardens 

 from South America, some years since, it was found necessary for their 

 preservation during transport to pack them in cotton, like jewelry. 

 Raphides are probably to be considered as non-essential results of the 

 Vegetative processes; being for the most part produced by the union of 

 organic acids generated in the plant, with mineral bases imbibed by it 

 from the soil. The late Mr. E. Quekett succeeded in artificially pro- 

 ducing raphides within the cells of Rice-paper ( 351), by first filling 

 these with Lime-water by means of the air-pump, and then placing the 

 paper in weak solutions of Phosphoric and Oxalic acids. The artificial 

 raphides of Phosphate of Lime were rhombohedral; while those of 

 Oxalate of Lime were stellate, exactly resembling the natural raphides of 

 the Rhubarb. l 



360. A large proportion of the denser parts of the fabric of the higher 

 Plants is made up of the substance which is known as ligneous tissue or 

 woody fibre. This, however, can only be regarded as a very simple vari- 

 ety of cellular tissue; for it is composed of peculiarly elongated cells 

 (Fig. 259), usually pointed at their two extremities so as to become 



1 The materials of the above paragraph are derived from the excellent section on 

 this subject in Prof. Quekett's " Lectures on Histology." Besides the Vegetable 

 structures therein named as affording good illustrations of different kinds of 

 Raphides, may be mentioned the parenchyma of the leaf of Agave, Aloe, Cycas, 

 Encephalartos, etc. ; the cuticle of the bulb of the Hyacinth, Tulip, and Garlic, 

 (and probably of other bulbs); the bark of the Apple, Cascarilla, Cinchona, Lime, 

 Locust, and many other trees; the pith of Eleagnus, and the testa of the seeds of 

 Anagallis and the Elm. The Raphides characteristic of the different Natural 

 Orders of Plants were carefully studied by Mr. Gulliver; who gave an account of 

 them in successive Papers in "Ann. Nat. Hist.," 1861 et seq. 



