A rid Regions of Western China. 1 1 09 
Let us lastly consider the xerophytic flora in general, noting that one 
of its most constant features is the 6 rosette J habit. 
It is well exhibited by Didissandra lanuginosa and other species 
(10,000-12,000 feet), Androsace Bulleyana (9,000-11,000 feet), Saxifraga 
candelabrum (10,000 feet), and even Eremurus chinensis (9,000 feet) with 
its rosette of stiff spear-like leaves. 
It is scarcely necessary to point out that the ‘ rosette 5 habit is not 
peculiar to xerophytes, being common for example on lawns ( Taraxacum , 
Beilis ), where it is doubtless brought about by the necessity for exposing as 
much surface as possible in a limited space, or to mutual pressure of parts. 
But when the most successful plant of all found growing under 
abnormal conditions adopts a peculiar habit, and when moreover this 
identical habit is found in several other plants growing under similar 
conditions, we are justified in believing that this habit is in fact an 
adaptation to withstand those conditions. 
Thus the most characteristic plant of all, growing in the semi-desert 
and arid valleys down as low as 7,000 feet, is Selaginella involvens> which 
covers the rocks in its thousands. 
The c rosette ' habit protects the plant to a considerable extent against 
undue transpiration, the small, closely packed and overlapping leaves 
shading one another and forming an admirable protection for the growing 
point ; moreover, the resulting dwarfed habit implies a minimum exposure 
of the plant to the desiccating winds, and is doubtless largely due to the 
brilliance of the direct and reflected light. 
But the Selaginella referred to amply protects itself throughout the 
driest weather by rolling up into a ball like a hedgehog, thus exposing only 
the under surface of the leaves, which is silvery. Almost exactly the same 
device is adopted by the Fern Cheilanthes farinosa , each frond of which 
curls up into a little ball during the dry season, exposing a brightly silvered 
surface. It will probably be found that this surface, by reflecting the light 
and heat rays, reduces still further the transpiration from the under sides of 
the leaves. 
Other familiar adaptations are fleshiness, found in several species 
of Sedum (stem and leaves), besides Opuntia , and the very thick cuticle of 
Eremurus ; we need say nothing about them. But it may be noted that 
the ‘ rosette ’ habit often carries with it a biennial existence, e. g. Androsace 
Bulleyana and Saxifraga candelabrum , the first year being employed 
in storing the rosette with reserve food for the final effort of flowering 
in the second. 
Finally, we may point out that there are not a few plants characteristic 
of the higher arid valleys which present none of the above obvious pecu- 
liarities ; such are Amphicome arguta and the twining Dregea sinensis \ 
But it is only fair to add that these are not found at the bottom of the deep 
