BY SELF-ADAPTATION TO THE ENVIRONMENT. 257 
XIII. General Summary of Observations on Desert Plants. 
Very many additional instances might be given in illustration 
of the preceding observations, but enough has been stated to 
bear out the contention, first, that we are justified in concluding, 
from innumerable coincidences between structure and environ- 
ment, that there is some common relation between them of cause 
and effect ; secondly, that all parts of plants are subject to varia- 
tions, and that while, on the one hand, they may be merely 
casual, accidental, transient, and of no classificatory value wbat- 
ever, yet on the other they may become more and more per- 
sistent and characteristic, and thence hereditary; affording the 
systematist features which he may pronounce as varietal or 
specific, as the case may be. Lastly, seeing how by experimental 
evidence plants can lose or take on such characters according 
as they are grown away from or in the normal environment, 
with which they are associated, the cumulative evidence amounts 
practically to a demonstration that varietal and specific cha- 
racters are solely acquired through the direct action of the 
elvironment. 
XIV. Self-fertilization of the Flowers of Desert Plants. 
In walking along the dry watercourses or “ wadys”’ of the 
deserts around Cairo, one cannot fail to notice the almost entire 
absence of conspicuous flowers. This fact is correlated with the 
paucity of insects. Ona closer inspection it is found that a great 
many, probably the large majority, of flowers are self-fertilizing, 
the process of pollination being often associated with certain 
degenerate conditions of the organs of the flowers, as compared 
with allies of other countries which are adapted to insect 
Visitors. | 
In my paper on “Self-Fertilization” * I drew up a list of 
characters some one or more of which are to be found in 
numerous weeds of cultivation and other plants which are 
habitually autogamous. Several of these conditions are charac- 
teristic of the flowers of Desert plants as well as other special 
features not therein mentioned. 
The general conclusion arrived at by a study of the flowers of 
the Desert is in complete accordance with those I have elsewhere 
givent; namely, that flowers which have been adapted to insects, 
* Trans, Linn. Soe. ser. II. Bot. i. (1879) p. 317 ete. 
+ ‘Origin of Floral Structures,’ Chaps. xxvi. and xxvil, 
