54 TREE GROWTHS IN WATERLESS TRACTS. 



of moisture in districts which appear to be and in fact 

 are otherwise entirely waterless. Most of the desert 

 grasses and other herbage possess similar powers, and 

 where the sand is deep and the soil porous, there does 

 not seem to be any practical limit to the depths to which 

 their fine, hair-like rootlets may not penetrate. 



Personally we have always held to the opinion that 

 where considerable quantities of arborescent growths 

 are found existing in apparently waterless tracts, it is 

 an almost certain sign that water will generally be 

 discovered by digging at no very great depths beneath 

 the surface (for wells) above all, if upon examination 

 of the twigs of these shrubs, it is found that they 

 produce moderately long season-shoots of young wood. 

 These opinions, we may add, have recently been to a 

 great extent borne out by the results of borings made 

 in the Kalahari, the French Sahara, and other desert 

 regions. 



Mr. Darwin also points out that probably this class 

 of food represented by twigs etc., cropped from the 

 desert bush, " contains much nutriment in a small bulk." 

 This is now an ascertained fact ; and he calls our atten- 

 tion to the well-known case of the camel, an animal of 

 no mean bulk, which has always been an emblem 

 of the desert. And as we know, the camel obtains 

 its nourishment from dry twigs, and tufts of dusty 

 grass, and other desert products of the most appar- 

 ently indigestible and unpromising character. 



According to the Encyclopedia Britannica elephants 

 in Africa are almost exclusively tree-feeders espe- 

 cially of mimosas. 



Some of the largest birds too, follow the example 

 of the quadrupeds, and are found only on desert plains 



