DEVELOPMENT AND DISTRIBUTION OF THE LEGUMINOSZ. 395 
Upon the separation of Australia from Asia and Africa, 
and the strong differentiation of climate either in Post- 
Cretaceous or Post-Hocene time, a marked change ensued 
in the morphology of the genus Acacia. Within the 
Americano-African tropics the Vulgares developed along 
parallel lines with the genera Mimosa, Calliandra, and Inga. 
None of these, however, reached Australia. In Vulgares 
the spinescent stipules of the primitive Acacia were sup- 
pressed in favour of the development of scattered prickles, 
while in this section, as also in Gummifere, a response was 
made to harsh climatic and soil environment by the reduc- 
tion of the leaflet surfaces, as well as by other means, such 
as the secretion of gums. In this manner the genus was 
enabled to occupy the sub-arid and poor lands, both within 
and south of the shrunken megathermic area in Post-Cre- 
taceous and Post-Hocene time. 
It was in Australia, however, that the most successful 
adaptations to inhospitable surroundings were secured by 
the genus. The great morphological modifications which 
produced Kucalyptus and the pbyllodineous Acacias appear 
to have been contemporaneous, and due to the same cause; 
the one being a local alteration of a uniform primary type 
without the development of a new genus, the other a 
modification so profound as to have given rise to a peculiar 
genus, famous throughout the world for its vitality and its 
economic value. In each case a vigorous and aggressive 
type was formed, the association of the two giving a 
distinct facies to the Australian forest proper, as well as 
to the scrub lands, but not to the jungle or brush growths, 
however, these being formed of types older, in the main, 
than either Hucalyptus or the endemic species of Acacia. 
In Australia the Gummiferze do not appear to have 
established themselves very securely, inasmuch as they 
appear there tobe decadent. A great response was made, 
