114: REPORTS ON THE STATE OF SCIENCE. — 1915. 



' Bloodwood ' group which has been indicated as containing the earlier 

 forms of Eucalyptus by reason of their oil-contents (7) by I'eason of the 

 antheral classification of the genus by Bentham (26) and by their 

 general appearance also, as shown by Oambage (1) and the writer (27). 

 In the second place, the genus Eucalyptus has all the biological 

 signs of youth. It is vigorous and aggressive; it is rich in species; 

 and it is the dominant vegetation of the continent of Australia. It 

 occurs in every geographical situation; it swarms on the great sub-arid 

 plains of the interior ; it forms thickets on the barren sandstone ; it 

 survives the desolating winds of the colder plateaus ; it flourishes in 

 the I'a vines of the plateau margins ; it grows in the swamps ; and it 

 advances almost to the very intersection of the planes of sea and land. 

 As opportunity offers in other continents, it quickly establishes itself 

 therein. Only in the jungle has it failed to establish itself. Were it 

 a genus which had once been cosmopolitan, as asserted by Ettings- 

 hausen (28), now decadent, it would be represented by monotypic 

 and oligotypic genera scattered in various isolated localities with wide 

 stretches of intervening areas containing no representatives of the 

 genus. On the other hand, it is not only overwhelmingly rich both 

 in species and individuals in Australia but it is also excessively 

 tenacious of life and adaptable to its environment. This suggests that 

 it is a specialised form peculiar toi Australia, much as the vast genus 

 Myrcia is to tropical and subtropical America. 



In the third place, the earlier life history of Eucalyptus suggests 

 that it is a specialised form of the fleshy-fruited Myi'tacete. Only in 

 the juvenile forms of the genus are the leaves consistently opposite 

 and penniveined, as in the fleshy pantropical forms. In many species 

 of the genus these generalised leaf types are obstinately persistent as 

 in E. cinerea, E. cordaia, and E. pulver-ulenta. The obstinate per- 

 sistence- also of juvenile cordate, sessile, and horizontal leaves in the 

 genus indicates that such leaf-types had been strongly established for 

 a very long period in the family before the evolution of the genus 

 Eucalyptus ; and that the latter, typical Eucalyptus leaf, with twisted 

 stalk, is an adaptation to a harsher climate and one which would tend 

 to become extinct, in favour of the old persistent type, under certain 

 favourable climatic conditions. 



In the fourth place, the genus Eucalyptus appears to be a modifica- 

 tion of a warmth -loving plant to meet varying conditions of dryness 

 and coldness; as such it indicates a more youthful origin than that of 

 the luxuriant and megathermic Myrtse. 



In the fifth place, the vast genera Eugenia and Myrtus have been 

 enabled to occupy all the fertile tropics even in lands so widely isolated 

 as Tropical America, Africa, Asia, and Australia. The morphology and 

 habits of these luxuriant types suggest a former land connection 

 between the great tropical lands. But these land bridges, if existent, 

 do not appear to have been used by tihe genus Eucalyptus, and the 

 only explanation possible, in view of the great vigour and tenacity of 

 the genus, is that Eucalyptus was developed only after the separation 

 of the great tropical lands from one another, whilst the Myrtse were 

 developed prior to such separation. 



