353 



Dr. Willis emphasises the statement that by the use of the hypothesis of Age and 

 Area, one is able to discover new facts which may lead to advances in our knowledge 

 of geographical distribution. Natural selection cannot do this. 



De Vries' review is charmingly written, and one of the most lucid and convincing 

 presentations of Dr. Willis' thesis of " Age and Area " I have seen. 



Considering some of the species of most circumscribed range (so far as we know 

 them), let me remind my readers (and we all constantly require this reminder) that, 

 as regards distribution of species, Australia is a very imperfectly explored area and, 

 as the days roll on, most important data, modifying our present knowledge of distribution 

 will inevitably become available. Further, those few " species " that we only know 

 in the juvenile leaf stage, or as having scarcely progressed beyond it, may be traced 

 as evolutionary forms of other full grown "species." In such cases (when proved) 

 the areas of the " complete " species will be that of the combined areas of juvenile 

 and full-grown species. But this is an interesting by-path, not influencing the range 

 of species in general in an important manner. 



I consider this an important path of research. If, say, twenty species (Willis's 

 m inimum) in juvenile leaf stage can be found to have restricted areas, it would go a long 

 way towards proving, on the hypothesis of Age and Area, that this was the earliest 

 form of Eucalyptus. 



Turning to Australian species of limited area (sometimes (?) erroneously called 

 " disappearing " species), we must differentiate between those in botanically well- 

 explored areas and those in areas which, when better explored, may tell a different tale. 

 Let us consider the following : — 



1 . E. pulverulenta. 5. E. Abergiana. 



2. E. Staigeriana. 6. E. Pimpiniana. 



3. E. Cliftoniana. 7. E. Kruseana. 



4. E. argillacea. 



In this short list, Nos. 1, 4 and 7 have predominantly juvenile foliage, and the fact 

 that they have not attained the falcate or mature-leaved stage is an argument in favour 

 of the hypothesis that they are recent arrivals. 



It may be mentioned that the localities of all these species are more or less 

 difficult of access, at least to workers in the capital cities. 



In contrast with these we may take, as examples, our two most widely diffused 

 species, viz., 



E. rostrata. E. microtheca. 



Some years ago I inclined to the view that a species like E. pulverulenta, only sparsely 

 known from a few hill-tops and a few specimens, was a depauperate and disappearing 

 species, related to or descended from a species we are still uncertain about. 



