BY SELF-ADAPTATION TO THE ENVIRONMENT. 221 
dry all the year round excepting in February and March, while 
no plants occur on the higher ground at all,—the general 
appearance is of low bushes or isolated tufts of a nearly uniform 
grey colour. The plants are never crowded or cover the ground 
like an English roadside. In other words, they do not struggle 
for an existence with one another, but only with their inhos- 
pitable inorganic environment*. The grey colour is mainly 
due to intense hairiness, which subdues the green hue of chlo- 
rophyll. A few plants only, comparatively speaking, have 
no hair, and are consequently greener, as the species of 
Zygophyllum, which are fleshy-leaved plants; but a coating 
of wax is of frequent occurrence, and this aids in giving a 
glaucous hue. 
The hair and the wax, as well as the fleshy character of the 
leaves, are adaptations to arrest the loss of water by transpi- 
ration during the summer. 
IIT. Spinescent Characters. 
The next obvious feature is the stunted character of the 
bushes, three feet being about the maximum height (Zilla mya- 
grotdes), with gnarled stems at the base. This is often coupled 
with a spinescent character, either in the branches (as Zila), 
foliage (as Echinops), or stipules (Fagonia) and bracts (Cen- 
taurea). These features are, we may say undoubtedly, in the 
rest I am greatly indebted to the kindness of Prof. E. Sickenberger, of the School 
of Medicine, Cairo; so that I have been able to examine anatomically nearly the 
whole series described by Dr. Volkens, and have thus been able to supplement 
his observations in some degree in points he has not recorded. I would also 
refer the reader to the writings of M. P. Maury, Assoc. Frang. pour I’A vance- 
ment des Sci., Congrés de Toulouse, 1887 ; also Morot’s Journ. de Bot. ii. 1888, 
Rev. Bibl. p. 101. 
* Similarly of the desert regions of Beluchistan, Dr. Aitchison says — 
‘‘The barren character of the country and the want of indigenous trees 1s 
due to the extreme dryness of the soil and aridity of the atmosphere. wee 
The struggle of plant-life for existence is great. The plants which are 
seen to exist through it all are either annuals or those possessing great 
root-stocks, tubers, tuberous roots, rhizomes, bulbs, or other such structural 
developments as assist them to baffle and survive through the extremes of 
temperatures.”—‘“A Summary of the Botanical Features of the Country tra- 
versed by the Afghan Delimitation Commission during 1884-5,” Trans. and 
Proc. Bot. Soc. Edinb. 1889 (read April 11th, 1889), p. 42. 
