136 BOTANY 
once had small thin leaves suited to a warm moist 
habitat, and became modified to its present form an 
response to changes of climate resulting in drier 
conditions; for a plant, in its individual development, 
sums up the history of the development of the type to 
which it belongs. 
The dense felt of slender woolly hairs that covers 
the exposed parts of the vegetable sheep (Raoulia) not 
only reduces the loss of moisture by impeding the 
escape of the transpired water, but, by forming a non- 
conducting layer, protects the plant, as by a blanket, 
against excessive heat and cold. 
In the tauhinu, a small shrub common all over the 
gum lands, the leaves are rolied back to form a wind- 
still tube from which the transpired water does not 
readily escape. In a_ similar way, to prevent wilting, 
erass leaves in the young stage are folded to enclose 
the stomata; but, as the epidermis thickens, they 
unfold and assume a more horizontal position to 
receive the rays of light. 
Soil water is conserved by creeping and rosette 
plants, which, by their shade, prevent evaporation 
from the surface. The spinifex and calystegia of the - 
sand dunes are good examples of the former, whereas 
the plantain, dan@€lion, and cat’s-ear illustrate the 
latter. 
Cushion plants, too, like the vegetable sheep just 
mentioned, also shade the soil. 
Protection of Leaves.—Already we have seen how 
bud scales and exudations of sum prevent the tender 
leaves from drying out, and how, in the vegetable 
sheep and many other alpine plants, a hairy surface 
Serves aS a protection against heat and cold. In the 
brier and Seoteh thistle, again, the spiny leaves act as 
a safeguard against grazing animals, while doubtless 
the unpleasant taste of the poppy and poisonous nature 
of the ragwort serve the same purpose. The leaves of 
