Genera Cei'aria and Portulacaria. 
1 1 1 3 
only to be seen with difficulty, and with a low-power objective the outer and 
inner walls alone are visible. The guard cells (PI. XCVIII, Fig. 2) are 
spherical in section, and are accompanied by two subsidiary cells (PI. XCVIII, 
Fig. 3) placed parallel to the pore. A peculiar feature of the leaf is the 
occurrence of calcium oxalate crystals in the intercellular space beneath 
several of the stomata. 
De Bary 1 and Sachs 2 both cite a few cases in which calcium oxalate is 
present in the cell-walls of the epidermis, though the formation of crystals 
of this substance in intercellular spaces is unrecorded by them. According 
to Sachs the occurrence of calcium oxalate in the cell-walls is rare among 
Angiosperms, only having been observed by Solms-Laubach in certain 
species of Mesenibryanthemum and in Semper vivnnt calcareum . Pfeffer has 
recorded the occurrence of these crystals in the cell-walls of some Dracaenas, 
and in these cases calcium oxalate is not confined to the epidermis, but is 
found also in cells lying deeper in the tissue. On the authority of Solms- 
Laubach it is stated that these crystals occur commonly in the Gymno- 
sperms, being formed in the middle lamellae of the cell-walls. No indication 
of a similar origin of the crystals in Ceraria is given. No definite palisade 
tissue occurs, the outer cells of the mesophyll containing numerous chloro- 
plasts. These decrease in number as the centre of the leaf is approached, 
though none of the central cells is devoid of them. Below the epidermis, 
large brown mucilage cells are found in which there are no chloroplasts. 
In this species the mucilage cells occur scattered in the first two rows of 
cells beneath the epidermis. The vascular bundles are small in section and 
vary but little in size. There are from seven to eleven bundles in a leaf, 
and these are deeply embedded in the tissues, so being invisible from the 
outside. The appearance in transverse section is that of a parallel-veined 
leaf, but it can be shown by cutting a section in the plane of venation that 
the bundles form a loose reticulum. Each bundle leaves the primary vein 
at a small angle, and almost immediately assumes a direction parallel to 
that of the central bundle. At the tip all the bundles branch and 
anastomose, so giving rise to a complex network. 
Clustered crystals of calcium oxalate occur in the mesophyll. There 
are two kinds of these crystals. The first has a rough sandy appearance, 
due to the fact that all the crystals in a cluster are not of the same length 
and some project beyond the others, so giving the whole mass, when highly 
magnified, a spiny appearance. These crystals resist the action of nitric 
acid longer than the large crystals which are found beneath some of the 
stomata. This second kind of cluster is made up of a large number of 
slender wedge-shaped crystals, radiating from a centre and so forming 
a hemispherical mass. 
4D 
1 De Bary (’84), p. 102 (1). 
2 Sachs (’82), p. 66 (4). 
