BY SELF-ADAPTATION TO THE ENVIRONMENT. 219 
so that these several countries afford either the same or “ represen- 
tative plants,” one infers (but of course at first merely on @ priori 
grounds) that most probably similar causes have produced these 
similar results. A closer inspection shows that the similarities in 
the vegetative system of such plants, which often have no affinity 
between them whatever, can be carried down into the minutest 
details of histological structure; and that a large proportion 
of such structures at least are always serviceable to the plants 
in resisting the deteriorating effects of an insufficient supply of 
water, as well as of an excess of radiation and other hindrances 
to such vigorous growth as is maintained in moister climes. 
We thus begin to suspect, indeed very strongly, that the 
various peculiarities (such, e. g., as the densely hirsute clothing 
and the consolidation of the mechanical tissues) are the direct 
results of the dry climatal conditions surrounding the plants ; 
and that the unfavourable environment actually brings about 
the production of just those kinds of structure which are best 
able to resist the injurious effects of the climate, and so enables 
the plant to survive under them. Such, at least, is the result 
of my own observations on the plants of the Egyptian deserts. 
The distribution of similar forms of plants under similar con- 
ditions illustrates another fact. We speak of ‘“ chalk-loving,” 
“‘sand-loving,” and other kinds of plants frequenting special 
environments ; but these phrases seem to be, to a great extent, 
misnomers. Plants by no means all or always “love”’ the soils 
alluded to, in which they are often found. Many flourish quite 
as well, if not better, in a totally different soil. Having, how- 
ever, been located in them for many generations, they have 
become so adapted to the peculiar conditions of the soil and 
climate, by assuming such structures as are the best under the 
circumstances, that they now succeed in them; but at the same 
time many are always tacitly protesting, so to say, against their 
environment; for they at once show how much more vigorous 
they can become when they are grown in a different and more 
congenial soil *. 
Similarly we might just as well speak of desert-loving plants, 
corresponding to the term “ xerophile;” but we xnow what an 
intense struggle for existence they have to maintain. Never- 
theless they have become so inured to their difficulties, that 
* See Battandier’s observations, Bull. Soc. Bot. de Fr. 1887, p. 189 
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