696 MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



Deposits of mineral matter in a crystalline condition, known as 

 rajtlndes, are not nnfrequently found in vegetable cells, where they 

 are at once brought into view by the use of polarised light. Their 

 designation (derived from pact's, 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 cells ; such bundles are well seen in the cells lying 

 immediately beneath the epiderm of the bulb of the medicinal 

 squill. It does not apply, however, to other forms which arc- 

 scarcely less abundant ; thus, instead of bundles of minute needles, 

 single large crystals, octahedral or prismatic, are frequently met 

 with, and the prismatic crystals are often aggregated in beautiful 

 stellate groups. The most common material of these crystals is 

 oxalate of lirne, which is generally found in the stellate form ; and no 

 plant yields these stellate raphides so abundantly as the common 

 rhubarb, the best specimens of the dry medicinal root containing .-is 

 much as 35 per cent, of them. In the epiderm of the bulb of the 

 onion the same material occurs in the octahedral or the prismatic 

 form. In other instances, the calcareous base is combined with 

 tartaric, citric, or malic acid ; the acicular raphides consist almost 

 invariably of oxalate of lime. Some raphides are as long as -^th of 

 an inch, while others measure no more than -j-^th. They occur in all 

 parts of plants the wood, pith, bark, root, leaves, stipules, sepals, 

 petals, fruit, and even in the pollen. They are always situated in 

 cells, and not in the intercellular passages ; the cell-membrane, how- 

 ever, is often so much thinned away as to be scarcely distinguish- 

 able. Certain plants of the ('tirf/m tribe, when aged, have their 

 tissues so loaded with raphides as to become quite brittle, so that 

 when some large specimens of C. senilis, said to be a thousand year- 

 old, were sent to Kew (lardens from South America, some years 

 since, it was found neccssarv for their preservation during ti'ansport 

 to pack them in cotton like jewellery. Raphides are probably to be 

 considered as non-essential results of the vegetative processes, being 

 tor the most part produced by the union of organic acids generated 

 in the plant with mineral bust's imbibed by it from the soil. The 

 late Mr. E. Quekett succeeded in artificially producing raphides 

 within the cells of rice-paper, 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. Besides the struct ures ;dre;idy mentioned as affording good 

 illustrations of different kinds of raphides, mav be mentioned the 



pareiichyi >f the lea f of Ai/nrr. .I/or, <'//ni. Encephalartos, etc.; 



the epiderm of 1 lie bull) of the hyacinth, tulip, and garlic ; the bark of 

 the apple. < '<tNCtiril/(f. < 'i iii-Iiniin. lime, locust, and many other t rees; the 

 pit 1 1 of i'.ln injii nx. and the testa of l he seeds of . I inii/iiHis and the elm. 

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

 plants is made up of the substance which is known as wood/y fibre or 

 prosenchymatous lisum-. Tin's, however, can only be regarded as a 

 variety of cellular tissue ; for it is composed of peculiarly elongated 



