52 
leaves of such, not being deciduous, are protected by many 
interesting devices from the influence of the dry air and hot 
sunshine of summer, which directly' tend to induce transpiration 
and rob the plants of their moisture. The leaves of the eucalypti, 
acacias, and others are set in a vertical position, so that their 
surfaces will be parallel to the sun’s rays at the hottest time of 
the day, and so receive less heat. In others the leaves are covered 
with hairs, especially on the under surface, and sometimes they, 
or the whole plant, are enveloped in a covering of hairs so dense 
and so matted together as to resemble thick flannel or blanket. 
Such a covering not only protects the substance of the leaf from 
excessive heat or cold or other injurious influences, but it may 
retain for a considerable time such moisture as may come to it 
from rain or dew, to the benefit of the plant. During the growing 
season leaves may? be somewhat soft and delicate, but with a 
gradually increasing intensity of sunshine and dryness of the air, 
the superficial layer of cells forming its substance may become 
thickened into an impervious cuticle, fireventing evaporation 
of the moisture below, and modifying the effects of the light and 
heat of the sun. In other cases fluids are excreted on the surface 
of the leaf, so that the epidermis is protected and the stomata 
effectually sealed with wax, gum, resin, or lime, In some leaves 
the stomata are so deeply sunk below the surface as to be removed 
from the direct action of the light and heated air, or they may 
be situated in the bottom of grooves which themselves become 
shrunk and partly closed when the air is dry. In some grasses 
and sedges you may observe that as they grow the leaves are 
quite flat, but shortly after the stalk is plucked you find that the 
leaves have lost their flat character and appear curled up length- 
wise, the change being due to the stoppage of the sap current 
when the stem was severed from the roots. One of the plants 
which come into flower about Perth in spring is Grevillea oxystigma, 
a small shrub with abundance of white blossom. As long as the 
rainy season lasts the leaves are mostly flat, but at a later date, 
in the dry' season, they appear more often as double-barrelled 
tubes, each half of the blade having curved backwards to the 
midrib, as if to exclude the dry' air from the under surface, which 
is already protected by a covering of minute hairs. This rolled 
condition appears to be more constant in the drier districts of 
the interior, such as Kellerberrin or the Stirling Ranges, while 
in these localities other species of Grevillea show the peculiarity 
in a still more pronounced degree. The rolling back of the marg- 
ins is often so tightly effected in some plants that the leaf must 
be broken up in order to see the hidden under-surface. From 
this condition of the leaf it is only a step further to one that is 
quite solid with the under-surface obliterated and a groove mark- 
ing the position of the midrib ; and from that again we easily 
arrive at the terete form, as it is called, like a knitting needle, 
