BY HENRY DEANK. 471 



countries where they do not now exist, as they were then repre- 

 sentatives of an already ancient and widespread group of Conifers. 

 The objection raised is against the probability of there having 

 lived in those parts the peculiar dicotyledonous types of the 

 Australian region. 



There are further considerations which point to the great 

 improbability of the existence of Eucalyptus in the Cretaceous of 

 the Northern Hemisphere. Eucalyptus belongs to a natural 

 order in which the leaves are normally opposite. That the 

 ancestral forms of that genus possessed opposite leaves is inferred 

 from the fact of the leaves being so arranged in seedlings; in many 

 species the change to long and alternate leaves only takes place 

 after several years' growth; in some species, such as E. melano- 

 phloia, the opposite character persists throughout life. These 

 facts seem to point to the probability of the pendent, leathery 

 leaves alternately placed being an adaptation to conditions of 

 drought, and in support of this supposition it has been pointed 

 out that where species have failed to produce the vertically 

 hanging leaves, another expedient has made itself apparent, 

 namely, that they have not only become thick and leathery, but 

 protected with a coating of an oily excretion giving them a 

 glaucous appearance. The flowers themselves have lost the 

 power of producing petals except as such may be represented 

 in the deciduous operculum, and this gives a still stronger 

 hint of the whole plant having become modified in the course 

 of long ages to resist drought, whereas its closest congeners, 

 Tristania and Angophora, which have petals, are confined 

 respectively entirely to the coast districts or to damper 

 situations on the eastern side of Australia, not having 

 been able to penetrate very far into the droughty interior. 

 These being the facts, is it likely that a genus so highly 

 specialised to resist drought should have lived in Europe so far 

 back as the Cretaceous 1 There also arises the question, if Euca- 

 lyptus flourished in England and Europe in the Cretaceous and 

 Tertiary, and, if the Cosmopolitan theory is trustworthy, through- 

 out the world in the latter age, what possible conditions could 



