The South Australian Naturalist. 
4-3 
TJic existence of “plant communities” has long been recog- 
nised. d'he ordinal')’ observer has noted, for instance, that there 
is one scries of plants to be found in the moist vaile\ s of the 
Gippsiand bush, and quite another plant communit)' on the hill- 
tops of tlie same region; so also there Is one plant communit)' of 
the Queensland scrub, a riotous jungle of growth, and quite an- 
other irroup of plants found on tlie dry Mallee plains. 'I'he coastal 
scrub of the sand dunes embraces a plant community that is 
quite distinct from the vegetation of the adjoining lagoons and 
swamps. Even in so characteristic a plant province as the Mallee 
moreover, we find a number of distinct communities; there is one 
set ol plants on tlie limestone ridges, another on the gypsum flats, 
another on the salty swamp lands, and another In the sandy hol- 
lows. Broadly speaking, the botanists speak of .five great plant 
groups, as lar as ecolog)’ is concerneci: — ■ 
(a) Hydropliytes (Water Plants). — Those that grow in creeks, 
rivers, and swamps, wholh’ or partly submerged in water. 
(b) Hygrophytes (Moisture-loving Plants). — Those that live on 
marshes, ri\'cr sides, and other damp areas. 
(c) Xerophytes (“Dry” Plants). — Plants that have accommoda- 
ted themselves to conditions of droughts. In this class be- 
long most of our characteristic Australian bush plants, 
Mesophytes (Intermediate Plants). — Here we find the majority 
of British plants, those that show no special liking or adap- 
tation eitlier for drought or moist conditions. 
Tropophytes (Changing Plants). — Including deciduous plants; 
that is, those that lose their leaves in winter, and thus take 
on \mr\hng cliaracters, according to their seasonal environ- 
ment. 
\\ e are concerned in this note with the plants of arid Aus- 
iralia, and mainl)’ therefore, with the great group called the Xcro- 
pliytcs, or we may us the adjective to describe them, and say 
they are "xerophilous’’ plants, that is, lovers of dryness. 
In different countries diiferent meanings are attached to the 
words ‘klesert” and '"arid lands.’’ In the United States of Amer- 
ica, for instance, a general definition of arid lands includes all 
areas with a rainfall of less than 20 inches. This would never do 
lor nor sensitive Australian souls, for many of us shrink from the 
acknowledgement of an Australian desert. As a matter of simple 
fact, wc have In the Commonwealth a bigger proportion of desert 
and arid lands than any other continent. We should recognise, 
(1) Trans. Ro)T Soc., S A., \ ol. 48 (1924), p. 110. 
