Chap. IX] 



DESERTS 



613 



shoots remain green throughout the summer, producing fruits as large as 

 a child's head. It presents therefore the appearance of being protected 

 in an unusual manner against the loss of water. As a matter of fact, 

 however, severed shoots dry up in a few minutes. The extraordinary length 

 of the roots of the colocynth alone renders its existence possible in the 

 desert. A considerable length of root is to a more or less extent common 

 to all desert plants, and has attracted the notice of all travellers. 



'Often as I tried,' says Volkens 1 , 'to dig up old bushes of perennial 



Fig. 344. Flora of the Sahara. Alhagi manrorum, Medic. After Taubert in Engler und 

 Prantl, Die natiirlichen Pflanzenfamilien. 



plants to the extremity of their roots, I never succeeded in doing so. The 

 most that I could establish was, that the root was thinner at a depth of one 

 or two meters than at the surface of the ground. A specimen of Calligonum 

 comosum (Polygonaceae), hardly the height of one's hand, had a root as thick 

 at its base as one's thumb, 1 I meters lower down it was still as thick as one's 

 little finger ; one can therefore safely assume that, in this case, the length of 

 the subterranean part was at least twenty times that of the epigeous part. 

 Many other plants exhibit a similar relation, especially species of Acacia, 



1 Volkens, II, p. 7. 



