CRYSTALS IN THE CELLS OF PLANTS. 
67 
the crystals, so that the unpractised observer thinks that he still sees them. Fine 
granules are abundantly scattered through the thickened cuticle of Gymnosperms 
{Welwitschia^ Taxus baccaia, Ephedra, &c.) ; or, in other cases, well-developed small 
crystals (Bioia orientalis, Libocedrus Doniana, Cephalotaxus Fortunei^ &c.). 
Closely related to these deposits in the cell-wall itself are the clusters of 
crystals discovered by Rosanoff (Bot. Zeitg. 1865, 1867) in the pith of Kerria 
japonica and Ridnus conmitmis, and in the petiole of some Aroideae {Anihurium, 
Philodendron, and Pothos), which, lying in the cavity of the cell, are attached to 
the cell-wall by simple or branched threads of cellulose, and are even covered with 
a cellulose membrane. Pfeffer has shown that the large and beautifully developed 
crystals which occur in the leaves and branches of Citrus vulgaris, as well as in the 
bark of Salix aurita, Celtis auslralis, Rhammis Frangula, Acer opulifolium, the 
Lombardy poplar, beech, and oriental plane, are also enclosed in a cellulose 
membrane which is often quite thick, and united in its growth, in one or more 
spots, with the cell-wall. 
The Crystalline forms in which the calcium oxalate occurs in the cells of plants 
are extremely numerous, a result of the circumstance that this salt crystallises in 
two different systems, according as it is combined with six or with two equivalents 
of water. The calcium oxalate containing six equivalents of water of crystallisation 
(ca o| ^4 ^6 ^" ^ ^^-^ crystallises in the quadratic system, the fundamental form 
being an obtuse quadrate-octahedron (the shape of a letter-envelope) ; combinations 
of the quadratic prism with the obtuse octahedron are met with in abundance. The 
raphides, however, belong, as respects their behaviour in polarised light, according to 
Holzner, to the klino-rhombic system, in which calcium oxalate crystallises with two 
equivalents of water of crystalHsation (^^^ o| ^ ^*^")* fundamental form 
of the numerous combinations belonging to this class is a hendyohedron ; it produces 
derivative forms which are very similar to calcspar (as, for instance, in the deposits 
in the cell-wall), and others very similar to calcium sulphate. The clusters of 
crystals (sphere-crystals) may consist of individuals of one or the other system ^. 
a. As respects its physiological significance, calcium oxalate is a metabolic product 
which is of no further use to the plant, an excretion similar to the volatile oils, resin, 
and other substances which are often contained in glands. 
When the crystals remain so small that their volume appears inconsiderable in pro- 
portion to that of the cell itself, this latter may possess protoplasm capable of motion, 
nucleus, chlorophyll, and starch, as in the case of the hairs of Cucurbita or the mesophyll 
of Begonia. When, on the other hand, a crystal or a cluster or a bundle of raphides, 
or finally a mass of ^mall crystals, nearly fills up a cell, no other organised constituent is 
usually present. The cells which contain raphides have loosened walls which easily 
swell, and the bundles of raphides are generally surrounded by a thick gummy mucilage. 
Such cells, which serve as receptacles for crystals, may be compared to simple glands 
which contain volatile oils and similar substances. 
^ [Vesque has succeeded in reproducing artificially the crystalline forms in which calcium 
oxalate makes its appearance in vegetable tissues. Raphides are produced, according to his experi- 
ments, in the presence of glucose and also of dextrin. See Ann. des Sc. Nat., cth ser., vol. XIX. 
p. 310.] 
F 2 
