I I 2 
F. E. Weiss and R. H. Yapp. 
In addition to the features already mentioned, a few others 
call for attention. 
Fig- 22. Sarcocaulon Burmauni (slightly enlarged). 
Spiny Plants. 
The first of these is the spiny habit, which many of the Karroo 
plants, in common with those of other desert regions, possess. 
The spines may be of very different morphological nature in 
different cases. Thus, in Acacia horrida they are well-developed 
stipules, in Sarcocaulon Burmanni (Text-fig. 22) they arc modified 
leaves. Whole axillary shoots become thorns in Asparagus sp., 
and Euphorbia Hystrix .* In Mesembriantheinum spinosum (Text- 
fig. 19) it is some of the inflorescence axes which become modified 
as spines. 3 
While we do not wish to attempt the solution of the vexed 
question as to whether spines are to be looked upon as reduced 
structures, correlated with, and produced by, dryness of climate or 
other purely physical factors ; or, on the other hand, as organs of 
1 Rolus, loc. cit., p. 225. 
3 In most spiny Euphorbias the thorns are paired stipules; in 
E. hystrix their morphological value is the same as in E. 
vinmillaris, see Goebel, loc. cit., part I., p. 62. 
3 Chodat, in “ Une excursion botanique Alajorque ” 1905, p. 81, 
describes a spiny inflorescence in Sonchus cervicornis. 
