THE PLANTS OP THE KALAHARI. 87 



eighteen inches beneath, the root enlarges to a tuber, often as 

 big as the head of a young child, which, on the rind being 

 removed, is found to be a mass of cellular tissue, filled with fluid 

 much like that in a young turnip. Owing to the depth beneath 

 the surface at which it is found, it is generally deliciously cool 

 and refreshing. Another kind, named mokuri, is seen in other 

 parts of the country, where long-continued heat parches the 

 soil. This plant is an herbaceous creeper, and deposits under 

 ground a number of tubers, some as large as a man's head, often 

 in a circle, a yard or more horizontally from the stem. The 

 natives strike the ground on the circumference of the circle 

 with stones, till, by hearing a difference of sound, they know 

 the water-bearing tuber to be beneath. They then dig down a 

 foot or so and find it. 



But the most wonderful plant of the desert is the Kengwe, 

 the water-melon of the Caffres. In years when more than the 

 usual quantity of rain falls, vast tracts of the country are 

 literally covered with these juicy gourds, and then animals of 

 every sort and name, including man, rejoice in the rich supply. 



The creeping plants of the desert serve, moreover, a double 

 purpose ; for, besides their use as food, they fix, by means of 

 their extensive ramifications, the constantly shifting sands — 

 thus rendering similar services to those of the sand-reed {Ara- 

 raaphila arundinaced) on the dunes along the sandy coasts of 

 the North Sea. 



The Mesembryanthemums are another family of plants ad- 

 mirably adapted to the Kalahari, as their seed-vessels remain 

 firmly shut while the soil is hot and dry, and thus preserve the 

 vegetative power intact during the highest heat of the torrid 

 sun ; but when rain falls, the seed-vessel opens and sheds its 

 contents, just when there is the greatest likelihood of their 

 vegetating. This is the more wonderful, as in other plants heat 

 and drought cause the seed-vessels to burst and shed their 

 charge. 



One of this family possesses a tuberous root, which may be 

 eaten raw ; and all are furnished with thick, fleshy leaves, with 

 pores capable of imbibing and retaining moisture from a very 

 dry atmosphere and soil ; so that if a leaf is broken during the 

 greatest drought it shows abundant circulating sap. 



The peculiar and comparatively abundant vegetation of the 



