66 



MORPHOLOGY OF THE CELL. 



usually more or less completely fill up the cells, which are mostly elongated. Needles 

 of this kind arc formed also in great quantities when the leaves of many woody 

 plants change their colour and lose water by evaporation in the autumn, although 

 absent during the period of growth. 



Where the crystals lie in the cavity of the cell — and this is usually the case with 

 Angiosperms — they are commonly, perhaps always, coated by a thin membrane, 

 which remains after solution of the calcium oxalate, and must probably be con- 

 sidered as a coating of protoplasm. This is also the case, according to Payen, 

 even with raphides, and, according to the accurate observations of others, also in 

 the larger single crystals aAd clusters. 



In Angiosperms calcium oxalate occurs apparently only rarely deposited in the 

 substance of the cell-wall; Solms-Laubach (/.<:.) cites different species of Mesem- 

 bryanihemum {M. rhombeum, tigrinum lacerum, stramineum, 

 Lemanni) and Sempervivum calcareum, in which fine granules 

 or (in the last case) larger angular fragments of crystalline 

 calcium oxalate are scattered through certain layers of the 

 outer wall of the epidermal cells of leaves. Among Mono- 

 cotyledons, Pfeffer has observed well-developed crystals in 

 the thickened cuticle, and in cells which lie deeper in 

 the tissue, of Draccena rejiexa, arborea, Draco, and umbra- 

 culi/era. 



The occurrence of crystals of calcium oxalate in the sub- 

 stance of the cell-walls is, on the other hand, according to 

 Solms-Laubach, of common occurrence in Gymnosperms. 

 They generally consist of numerous small granules of un- 

 recognisable shape; not unfrequently, however, they are 

 well-developed crystals. In the bast- tissue of all parts of 

 the stem deposits of this kind are found in the Cupressinese, 

 Podocarpus^ Taxus, Cephalotaxus, and Ephedra ; they are 

 absent, on the other hand, from Phyllocladus trichomanoides, 

 Salisburia adianti/olia, Dammar a australis, and from all Abie- 

 tinese that have been examined. The small angular granules 

 or larger individual crystals are usually deposited in the soft 

 middle lamella of the walls between the bast-cells. Calcium 

 oxalate occurs still more widely deposited in the cell- wall 

 of the cortical parenchyma of the branches and leaves of 

 Gymnosperms, with the possible exception of some Abie- 

 tinese; here also the middle lamella of a common cell- wall 

 i^ the place where the crystals are formed, as also in the 

 bundles of thick-walled hypodermal cells {e.g. Ephedra). 

 The thick-walled often branched prosenchymatous cells 

 abundantly scattered through the parenchymatous tissue of Gymnosperms, the so- 

 called * Spicular cells,' not unfrequently contain crystals deposited in the outer layers 

 of their cell-walls ; these occur in unusually large numbers and great perfection in 

 Welwitschia mirabilis (Fig. 52). If the crystals are dissolved in hydrochloric acid, 

 the empty cavities in the substance of the cell-wall retain completely the form of 



Fig. 52.— Half of a spicular cell 

 of IVelwitschia tnirabili's, with a 

 great number of crystals of cal- 

 cium oxalate imbedded in the 

 outer layer of the very thick cell- 

 wall. 



