NATURAL HISTORY SOCIETY OF GLASGOW. 219 



stomata for the exhalation of watery vapour, which seem to be 

 necessary to plants in damp situations. On the other hand, 

 Mesembryanthemum edule has the additional contrivance of oblong- 

 tubers buried deep beneath the soil for complete protection from 

 the scorching sun, which serve as reservoirs of sap and nutriment 

 during those rainless periods which recur perpetually in even the 

 most favoured parts of Africa. Dr. Livingstone, speaking of the 

 region north of the Orange River, where the soil was light-coloured 

 soft sand, nearly pure silica, w r ith beds of ancient rivers containing 

 much alluvial soil, baked hard by the burning sun, says: — "The 

 quantity of grass which grows on this remarkable region is 

 astonishing even to those who are familiar with India. It usually 

 rises in tufts, with bare spaces between, or the intervals are 

 occupied by creeping plants which, having their roots buried far 

 beneath the soil, feel little the effects of the scorching sun. The 

 number of those which have tuberous roots is very great; and 

 their structure is intended to supply nutriment and moisture 

 when, during the long droughts, they can be obtained nowhere 

 else. Here we have an example of a plant not generally tuber- 

 bearing, becoming so under circumstances where that appendage is 

 necessary for preserving its life; and the same thing occurs in 

 Angola to a species of grape-bearing vine, which is so furnished 

 for the same purpose. The plant to which I at present refer is 

 one of the Cucurbitaceae, which bears a small scarlet-coloured 

 eatable cucumber. Another plant, named ' Leroshiia,' is a 

 blessing to the inhabitants of the desert. We see a small plant 

 with linear leaves and a stalk not thicker than a crow's quill; on 

 digging down a foot or 18 inches beneath, we come to a tuber, 

 often as large as the head of a young child; when the rind is 

 removed we find a mass of cellular tissue tilled with fluid much 

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

 the soil at which it is found, it is generally deliciously 

 cool and refreshing. Another kind, named ' Mokuro,' is 

 seen in other parts of the country -where long-continued heat 

 parches the soil. This plant is a herbaceous creeper, and deposits 

 underground a number of tubers, some as large as a man's head, at 

 spots 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 



