DESERT PLANTS 21 
very difficult conditions; yet there are few areas in 
which the eye will not note some strange vegetable 
form. In Fig. 3 are illustrated some of the remark- 
able Mesembryanthemums found in the South African 
deserts. Here the extremely fleshy leaves, arranged 
in opposite pairs, produce a sub-globular plant form, 
a mere mass of watery tissue, which in colour as well 
as shape appears to mimic the pebbles among which it 
grows. The frontispiece shows some other types of 
Fic. 3.—MESEMBRYANTHEMUM BOLUSII (LEFT), AND 
M. LESLIEI (RIGHT), BOTH %. 
desert plants. Another difficulty which desert plants 
have to contend with is this: continual evaporation 
from off the land of water charged with mineral salts 
— in some regions in bygone times, in others still 
following each brief rainy season—has left the soil 
highly impregnated with substances, of which 
common salt is one of the most abundant, which, ex- 
cept in very weak solutions, are deleterious to plant 
life, since water containing them is absorbed with 
difficulty by the roots. These old lake-bottoms and 
