BY SELF-ADAPTATION TO THE ENVIRONMENT. 235 
mentioned. This is a native of the Cape of Good Hope, and 
flowers in the winter, 7. e. July; but throughout the whole of 
the Mediterranean border, where it has become dispersed since 
1806, it blossoms from November to April *. 
Mr. Darwin has so fully discussed, under the head “Acclima- 
tization’’+, the variability of plants in adapting themselves to 
climate, and so becoming “ precocious” or “late” in flowering, 
that I need not enter upon this subject. All I would contend 
for is that such variations of habit are simply due to the respon- 
siveness of protoplasm to the environmental conditions, and that, 
when once acquired, they all tend to and may become hereditary 
traits. 
In corroboration of this I will conclude with the following 
observations by the late Dr. Lindley ¢:—‘ It often happens that, 
as in peas, the tendency in such plants to advance or retard 
their season of ripening was originally connected with the soil or 
climate in which they grew. A plant which for years is cultivated 
in a warm dry soil, where it ripens in forty days, will acquire 
habits of great excitability: and when sown in another soil will, 
for a season or so, retain its habit of rapid maturity; and the 
reverse will happen to an annual from a cold and wet soil. But 
as the latter will gradually become excitable and precocious if sown 
for a succession of seasons in a dry warm soil, so will the former 
lose those habits, and become late and less excitable.” 
VII. Histological Peculiarities of Desert Plants. 
Although the morphological features of desert plants are 
obviously adaptive, the histological elements illustrate the same 
fact even in the most minute details §. 
Eprpermis anp Curicte.—Commencing with the epidermis, a 
thickened cuticle in various degrees is of well nigh universal 
occurrence. There is also very frequently a superficial layer of 
wax. The cuticle is often covered with waved lines or ridges, 
especially on elevated cells, and the hairs with tubercles. 
* See my paper on “The Northern Distribution of Ovalis cernua, Thunb.” 
Proce. Linn. Soe. 1890-92, p. 31. 
t Animals and Plants under Domest. ii. p. 305. 
t ‘Theory of Horticulture,’ p. 465. (The italics are mine.) . 
§ The reader might consult M. Vesque’s descriptions and figures of species 
of Capparis, showing how their anatomical structure conformed to their habits. 
“ L’Espéce végétale considérée au point de vue de l'anatomie comparée,” Ann. 
Sci. Nat. sér, 6, t. xiii, 1882, p. 5. 2 ; 
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