Australian Flowering Plants. 199 



already mentioned on a previous page, furnished the Myrtaceie 

 with a chance for the development of xerophytic characters. 

 During the earlier zoning of the climate it is possible that 

 the important subtribe Metrosiderese has been developed in 

 the areas of good soils. At a period somewhat later the sub- 

 tribe Eucalyptese appears to have been developed, probably 

 from the Metrosiderese. Eucalyptus represents the adaptation 

 of a luxuriant type to hungry, sandy soils in a warm climate. 18 



"The obstinate persistence of juvenile, opposite, cordate, 

 sessile, and horizontal leaves in the genus, indicates that such 

 leaf-types had been thoroughly well-established for a very 

 long period in the family, before the evolution of the genus 

 Eucalyptus; and that the later typical Eucalyptus leaf with 

 twisted stalk is an adaptation to a harsher climate, and one 

 which would tend to become extinct, in part, in favor to the 

 old persistent type, under certain favorable climatic condi- 

 tions." 10 Moreover, the great size of the trees of the genus, and 

 their general appearance, proclaim the subtribe Eucalypteae 

 as a remove of no very great degree, from Myrtese, although it 

 must be borne in mind that the fruit is a capsule and not a 

 drupe. 



Like the phyllodineous acacias, Eucalyptus flourished first 

 on the moist, hungry, sandy soils. At a later date, when the 

 high plateaus were formed in the east, and when the great 

 inland plains were formed, Eucalyptus developed numerous 

 new species 20 to populate the fresh territory. This, however, 

 it was enabled to do only after becoming a vigorous and aggres- 

 sive type. All around Australasia it may be seen reaching 

 out arms, as it were, for new lands to conquer. The eastern 

 species offer never-ending puzzles to the systematists, many 

 types apparently being in a state of saltation, the species over- 

 lapping in the eastern plateaus, no intermediate areas being 

 unoccupied by the genus, it being prevented only from spread- 

 ing beyond Australia by reason of the wide ocean barrier 

 and the inability of the genus to grow in the jungle areas 

 of the neighboring islands. 



Meanwhile in Southern Australia, while the zoning of the 

 climate became more pronounced, other subtribes and even 

 another tribe of Myrtacese sprang into existence in the hungry, 

 sandy areas. These fresh types, as time progressed, became 



13 It. H. Cambage, The Distribution and Development of the Genus 

 Eucalyptus, Presidential Address, Proc. Roy. Soc. N. S. Wales, 1913. 



10 E. C. Andrews, The Distribution and Development of the Myrtaceae, 

 Proe. Linn. Soc. N". S. Wales, vol. xxxviii, p. 555, 1913. 



20 E. C. Andrews, ibid., pp. 554-565. 



