ON SOME POINTS IN THE STEM-ANATOMY OF 
EUPHORBIA VI ROSA AND ALOE DICHOTOMA 1 
By W. C. WORSDELL 
I am indebted to Prof. H. H. W. Pearson for placing at my disposal 
material of the stems of a candelabra-like Euphorbia and of the arborescent 
Aloe dichotoma Linn., both growing at an altitude of about 4000 ft. in the 
region of the Karasberg in Namaqualand (German South-West Africa). I was 
requested to try and trace the origin of the conspicuous air-cavities which 
occur in the pith of the Euphorbia and in the secondary wood of the Aloe. 
The ground-tissue of the stem in succulent plants as a general rule consists 
of cells which are often water-storing and are usually compactly grouped with 
either no, or very small, intercellular air-spaces. Such, for example, is the 
state of affairs in the pith of the stem of Euphorbia Caput Medusae Linn., 
Aloe africana Mill., Kleinia, Stapelia, which I have examined. The air- 
spaces are, in all ordinary cases, just large enough to enable the cells to carry 
on their necessary respiratory functions. On the other hand, it would appear 
to be a phenomenon of great rarity for one and the same tissue to act both as 
a water-storing and an air-storing reservoir. Such a case, however, is afforded 
by the succulent stem-tubers of the myrmecophilous plants Myrmecodia and 
Hyduophytum 2 , whose water-storing- tissue is permeated by large air-cavities, 
with cork-lined internal surfaces which later become adapted to serve as the 
domicile of ants. 
There are, however, other species of arborescent Euphorbias in which the 
air-spaces occur. I have seen a living stem of E. neglecta N. E. Br. possessing 
very large pith-cavities, of E. procumbens Miller, with fairly large ones, of 
E. Dregeana E. Meyer, with very numerous small cavities in the pith, and of 
E. canariensis with indications thereof. I have also seen these pith-cavities 
very well-developed in dried material of E. Cooperi N. E. Br., E. grandicornis 
Goebel, and in a form doubtfully referable to E. triangularis ; also in some 
individuals, but not in others, of E. meloformis Ait 3 . In other species of 
succulent Euphorbias the cavities are entirely absent. 
1 Percy Sladen Memorial Expeditions in South-West Africa, Report No. 27. 
2 Cf. G. Haberlandt : Physiologische Pfianzenanatomie ; 2nd ed. 1896, p. 349. 
3 I am indebted to Mr N. E. Brown for shewing me herbarium-specimens of these species 
at Kew. 
