P achy podium namaquanum , Welw. 933 
laticiferous cells occur in or accompanying the bundles. Outside each 
bundle is a number of pericycle fibres (f, Fig. 4), whose walls, which are 
very thick, give the cellulose reaction with iodine and sulphuric acid. The 
cortex is massive and fairly compact, composed of rounded parenchymatous 
cells, many of which contain calcium oxalate, a substance characteristic of 
the order. 1 It is found in highly refractive clustered crystals. Laticiferous 
cells are very numerous, traversing the cortex in all directions. Both here 
and in the pith they have thin walls and granular contents in which nuclei 
can sometimes be seen. These contents include proteid matter, which 
stains deep yellow with iodine and light yellow with nickel sulphate. The 
whole surface of the mature stem, protuberances, and spines is covered by 
a thick layer of tissue derived from a phellogen which arises in the second 
layer of the cortex. This tissue is suberized on the stem, but stains with 
haematoxylin on the young protuberances and spines. 
2. The Protuberances and Spines. 
(a) Structure of Protuberance. Each protuberance projects from the 
stem at approximately right angles to it (Fig. 1, A). A number of ring 
bundles pass out into the protuberance in the form of a narrowing hollow 
Text-fig. 4. Diagram showing the course of the vascular bundles through the protuberance. 
l.t. — leaf-trace ; i.c. = inflorescence supply. 
cylinder (Text-fig. 4). Some medullary bundles also pass out into the pro- 
tuberance, running up within the cylinder. On their way up, the ring 
bundles are joined by a few of the medullary bundles, which may branch 
off again. Beneath the level of the scar left by the inflorescence the cylinder 
of ring bundles can be seen dividing into two unequal portions : 
1. A trough of vascular tissue, with its open end upwards, bending 
1 Solereder ( 5 ), p. 530. 
