95 
XEROPHYTISM IN THE SWAN RIVER DISTRICT. 
By W. E. SiiKi/rox, 
(Head on V3th dune, 1921.) 
The term xerophyte is applied to plants capable of thriving 
in an environment unable to provide a normal plant with a 
sufficiency of suitable water. Such plants may be found in quite, 
widely differing regions. Hot deserts, arctic, antarctic and alpine 
lands, acid swamps, beach or salt-lake areas, all offer plants very 
limited supply of suitable water during* the w hole or a large part 
of the year. The ice-bound portions of the earth have no liquid 
water available for plants, while beaches, salt-lakes and swamps 
usually provide only water charged with injurious substances. 
The Western Australian hush is crowded with xerophyt.es. 
Our rainy season plants must not be included, however, Cor they 
either pass through the whole of their lives in the months of rain 
or else lie dormant underground as bulbs, conns, rhizomes or 
tubers during* the season m which their aerial portions are unable 
to withstand the hot drying influence of our summer sun. 
The xerophytic vegetation is of another type. It provides the 
permanent flora and comprises those plants which are able to with- 
stand the whole round of the seasons for perhaps many years. In 
our ten, nine, and even eight inch rainfall belts, dense assemblages 
of plants are found, here and there rising to the dignity of forests, 
and the plants so met are all able to flourish throughout the 
months of the year in which the precarious replenishment of water 
supply is dependent on occasional thunder showers. Even the 
poorly retentive sandy soils carry their cloaks of vegetation. 
The secret of this continued existence in such a forbidding 
environment is revealed by a study of the morphology and anatomy 
of the plants. Numerous departures from normal structure are 
to be noted and these are concerned with (a) absorption, (b) 
storage, and (c) loss of water. 
With regard to absorption, the root system is usually highly 
developed. Sometimes it is the great depths of the soil which are 
searched for water, while often an up-rooted gum tree shows an 
extended surface network of roots, eminently fitted to absorb 
rapidly the moisture from short summer storms. In addition, 
curiously modified hairs, capable of absorbing dew deposited on 
the plant surfaces, are occasionally to be seen. 
Water storage tissues are to be found in all parts of plants. 
Bullions roots such as those of Droseras, swollen stems of some 
salt-bushes 1 and fleshy leaves of the “pig-face,” 2 all furnish 
1. Salicornia Australis. 2. Mosembryanfchemum Aequilaterale. 
