BY SELF-ADAPTATION TO THE ENVIRONMENT. 229 
result as to the cause of the small size of the leaves of the 
“‘ ericaceous’’ type which prevails in parts of the Cape and of 
Australia. He observes:—“The climate [of the Karoo] is 
characterized by a long and dry summer and by plenty of wind. 
Such conditions obviously favour transpiration ... Hence the 
small and excessively coriaceous leaves of these plants without 
much spongy parenchyma are thoroughly suited to the climate. 
We may even, I think, go a step further and say that the 
physical conditions have produced this form... With regard to 
leaves certain observations, which are not yet extensive enough 
for publication, as to the variation in size and texture of the 
leaf in the same species in different habitats, strongly incline me 
to believe that the smallness, cuticularization, and want of spongy 
parenchyma in the leaf all follow directly from such conditions.” 
Similarly M. E. Warming attributes a similar result to climate, 
especially the dryness of the atmosphere on the Campos of Lagoa 
Santa in Brazil. He writes :—“ Lorsque les feuilles ne sont pas 
tomenteuses sur les deux faces, elles sont ordinairement raides 
et coriaces ; Jes feuilles de plusieurs espéces, agitées par le vent, 
font entendre un bruit de cliquetis ou de crécelle trés extra- 
ordinaire ; tels sont certains Salvertia, Vochysia, le Palicourea 
rigida ou strepitans et certains Bombax. La majorité des 
espéces arborescentes ont les feuilles dures et coriaces, 4 quelque 
famille qu’elles appartiennent” *. 
Besides the general reduction in size of the leaves, plants in 
the desert reach the subaphyllous and aphyllous conditions. The 
degradation in the size and form of the leaf passes through 
many degrees till the leafless stage is reached, as in Ephedra 
and Retama. Just short of that, the leaves are minute, scale- 
like, closely adpressed against the stem, and assume the ap- 
pearance of the foliage of Thuja, Cupressus, &e. In the desert 
this form is well seen in Anabasis reticulata and Salsola Pachot. 
Such leaves may terminate in sharp points, as in Cornulaca 
macrantha, and as seen in our English Salsola Kali. This last- 
named genus, as also Zamarix, adopts both forms, just as 
Retinospora may have them, even on the same plant. 
That drought is the main cause is inferred from the fact that 
similar forms occur in plants in rocky and arid mountain regions 
at high elevations. Thus while the New Zealand nearly 
* Op. cit. p. 155 [supra, p. 218]. 
