mace ree 
PLANTS OF THE SOTOL REGION 633 
(f. 9, wa) even when the covering is old and fissured. Structur- 
ally, there is much in common with the chitin-like cuticle of Avzo- 
carpus, even the interruption at the stomatal pits showing a ten- 
dency of certain striae to continue across, diaphragm-like. It is 
distinctly waxy, however, and soluble in alcohol. 
The epidermal cells themselves are small as in Ariocarpus and 
occupy about two irregular layers (f 9, ep). Here, also, the 
walls of these and of the first underlying assimilation-cells (/ 9, 
cu) are notably thickened to give a firmer binding of the epider- 
mis to the remaining tissues which the stress of alternating tur- 
gidity and flaccidity would tend to disrupt. The outer epidermal 
cells, at least, are ordinarily elongated with the stem-axis, but 
about the guard-cell apparatus they become box-shaped and more 
or less concentrically placed, forming a saucer-like depression at 
the bottom of which lies the guard-cell apparatus. The guard- 
cells proper are small and held in place above the ample air- 
chamber by two very large auxiliary cells which partially embrace 
the former (f. 9, g, 2). 
This stomatal structure recalls the case of Euphorbia Tirucalh 
of Zanzibar, figured by Haberlandt (Physiologische Pflanzenana- 
tomie, /, 762, 1896), in which the appearance of young branches, 
the waxy covering, the stomatal apparatus and the crater-like 
Openings in the wax above the stomata are all very similar to £. 
antisyphilitica, but Haberlandt’s figure appears to be diagrammatic 
merely, since the waxy covering is not so conspicuously built up, 
but only a slight elevation above the general surface of the thick 
coat as shown in /. 9. 
UNIVERsiTY orf TEXxas. 
