FROM THE RED SEA TO THE NILE 



D. T. MacDOUGAL 

 Desert Laboratory, Tucson, Arizona 



The measurement of the physical conditions which enter into any- 

 given environment and the estimation of their separate physio- 

 logical effects have come to form a very important part of geo- 

 botanical science. No part of this subject has a wider interest 

 than the matter of the light and moisture relations of organisms ; 

 and, by reason of the exceptionally favorable conditions under 

 which research upon these topics may be prosecuted at the Desert 

 Laboratory, no little amount of attention has been devoted to 

 them. 



It has been found profitable to carry out the detailed and exact 

 work of the Desert Laboratory at Tucson ; then to test the gener- 

 alizations reached, by brief \dsits to other arid regions. 



It was with no little anticipation that the author set out from 

 Cairo, in company with Mr. G. Sykes, in January, 1912, for the 

 purpose of making a traverse from the Red Sea across the inter- 

 vening mountain ridge, then down the gentler slope to the Nile; 

 after which, a. caravan was to be organized that would take us far 

 into the Libyan Desert. 



The journey was to begin in a maritime region with a monsoon 

 climate, where the annual total of nine inches is received in mid- 

 winter; and, within a few hundred miles to the westward of the 

 mountain barrier, a region would be penetrated in which the rain- 

 fall is so uncertain that it is, for the biologist, a feature of compara- 

 tively little importance: the supply for plants and animals being 

 derived from the ground-water; which is probably plutonic, or 

 derived from such distant sources as to be not identifiable as to 

 its origin. 



This interior desert, which stretches practically without inter- 

 ruption from the mountains near the Red Sea westward three 



243 



THE PLANT WORLD, VOL. 16, NO. 9, SEPTEMBER, 1913 



