66 
MORPHOLOGY OF THE CELL. 
usually more or less completely fill up the cells, which are mostly elongated. Needles 
of this kind are 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 and clusters. 
In Angiosperms calcium oxalate occurs apparently only rarely deposited in the 
substance of the cell-wall; Solms-Laubach {I.e.) cites different species of Mesem- 
bryanthemum {Af, rhombeum, tigrinum lac er um, stramineu?n, 
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 Dracmia reflexa, arborea, Draco, and imbra- 
culifera. 
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 Gymno.sperms. 
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 Cupressineae, 
Podocarpus, Taxus, Cephalotaxus, and ephedra; they are 
absent, on the other hand, from Phyllocladus trichomanoides., 
Salisburia adianlifolia, Dammar a australis, and from all Abie- 
tineae 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- 
tineae ; here also the middle lamella of a common cell-wall 
is 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 IVelioitschia 7nirabilis, with a 
great number of crystals of cal- 
cium oxalate imbedded in the 
outer layer of the very thick cell- 
wall. 
