Genera Ceraria and Portulacaria. 
1 1 19 
C. namaquensis , where the xylem shows no annual rings, the cork is not 
as distinctly layered as in C. gariepina favours this supposition. 
It is quite probable that when suitable material is obtainable, phello- 
derm may be found to be present, and in that case the position assigned to 
the cambium will be incorrect. 
Material for examining the apex of the stem of C. gariepina was not 
available, but as the formation of bark on the lower parts of the stem 
in this species is identical with that in C. namaquensis it is not probable 
that any differences of a serious nature are to be anticipated. 
In Portidacaria afra the bark is less strongly developed, but in the 
older stems it shows the same structure as in Ceraria. The phellogen 
arises in the epidermis (PL XCVIII, Fig. 12) and cuts off cells on the outside 
only, as in Ceraria. These cork cells are thin-walled but are not rectangular 
in outline, and become crushed almost as soon as they are formed. No band 
of cellulose cells separates the cambium from the cork (PI. XCVIII, Fig. 13). 
In Portidacaria afra , therefore, only one type of cork cell is found, while 
in Ceraria there are two. The stem apex is protected by two young foliage 
leaves and not by scale leaves as in Ceraria. 
The anatomy of the stem agrees very closely with that of Portidacaria 
afra (Text-fig. 4). The points in which these two genera differ may be 
tabulated as follows : 
CERARIA. PORTULACARIA. 
LEAF. 
1. Leaf club-shaped. 
2. Cuticle very marked. 
3. Palisade tissue slightly differ- 
entiated. 
4. Crystals beneath the stomata. 
1. Leaf flat and obovoid. 
2. Cuticle not conspicuous. 
3. Tissues not differentiated. 
4. N o crystals beneath the stomata. 
STEM. 
1. Thick bark of a peculiar struc- 
ture. 
2. Large water-storing cells in 
cortex. 
3. Mucilage cells in a ring and of 
a large size. 
4. Four medullary rays larger than 
the rest. 
5. Vascular cylinder occupying 
about one quarter of total area of 
stem as seen in section. 
1. Bark thinner but of same struc- 
ture. 
2. No water-storing cells. 
3. Mucilage cells forming a net- 
work in the cortex and of same size 
as rest of cortical cells. 
4. Medullary rays all of same size. 
5. Vascular cylinder occupying 
about one-third of total area of stem 
as seen in section. 
