Packypodium namaquanum , Welw. 931 
greatest ease by a pocket-knife. The large yellow flowers occur in June 
among the lower of the leaves which crown the stem ; in January the seeds 
are already scattered and only vestiges of the dried-up corollas remain’ 
(Text-fig. 1). 
1. The Stem. 
(a) External Appearance . A number of protuberances are arranged 
in a close spiral all over the stem (PI. LXXXIV, Fig. 1, A). At the apex of 
the stem each protuberance is seen to be situated in the axil of a leaf; the 
leaf soon falls off, and its scar is carried up the protuberance by subsequent 
growth at the base of the latter. The protuberances, when young, project 
from the stem at approximately right angles to it ; later they are recurved. 
On the lower surface of each is the leaf-scar (/. s. 9 Fig. 1, B), and on the upper 
Text-FIG. 2. Diagrammatic transverse section across the stem, showing the proportions 
of pith and cortex. 
surface a scar which is no doubt left by the inflorescence (i. s. 9 Fig. i,c). 
Each protuberance is fleshy and ends in three hard sharp thorns which bend 
downwards. The two lateral spines are longer than the median spine ; 
they arise nearer the back of the protuberance, and bend down more 
sharply, than the median spine. Occasionally four spines are found in 
a group, in which case the two inner are shorter than the outer. 
(b) Anatomy. The thickness of the stem is mainly due to the bulky 
pith (Text-fig. 2), the growth of which is almost entirely responsible for the 
increase in diameter of the stem. This growth is not caused by a cambium, 
but by the irregular division of the cells of the pith ; this is clearly seen in 
section near the stem apex. The pith is very complex, consisting of large- 
celled water-storing parenchyma, in which medullary vascular bundles and 
laticiferous elements run in all directions (Fig. 2). With the limited amount 
3 P 2 
