424 DISCUSSION. 



In looking over closely related pairs of Australian species of 

 plants, we find them growing not in closely adjacent districts 

 which are separated by some geographical barrier, but actually 

 growing side by side as we should expect when some form of 

 physiological isolation has been the chief factor in separating 

 them. For instance : Todea barbara and T. fraseri; Darwinia 

 fascicularis and D. taxifolia; Dillwynia ericifolia and D. 

 floribunda; Angophora lanceolata and A. intermedia; Epacris 

 pidchella and E. jyurpurascens — pairs of very closely related 

 species, more closely related to one another, apparently, than any 

 others of the same genus are found, not isolated but growing side 

 by side. Corresponding pairs of species of animals to wliich 

 similar remarks are applicable are — Macropus giganteiis and M. 

 robustus; Python s^nlotes and P. variegata; Amphibolurus bar- 

 batus and A. muricatus; Tiliqua scincoides and T. nigrolutea; 

 and many other such pairs, both of plants and animals, could be 

 readily mentioned. 



Dr. Chapman offered some theoretical considerations. 



Mr. Maiden instanced the genus PAce?-os/)/icera[N.O. CoNiFERiE] 

 a very local genus, one of whose species has a very limited range 

 on certain mountains in Tasmania, and the other on the Blue 

 Mountains of N.S.W. Dodoiuea filifolia of Queensland and New 

 South Wales, and D. ericifolia of Tasmania, probably had a 

 common ancestor which grew along the greater part of the entire 

 eastern coast of Australia. The genus Eucalyptus, which 

 includes m;uiy species, offers some which may fairly be looked 

 upon as geminate. Tlie E. stelhdata-Moorei, E. aviygdali7ia- 

 regnaus, E. amygdalina-dives pairs all grow together, without 

 obvious barriers. The E. Cambagei-goniocaJyx, E. polyantJiemns- 

 Mudderi pairs have localities which join on to one another, or 

 are separated by not a wide barrier. Tlie E. tereticornis-Seeatia 

 pairs grow together, but the E. tereticornis-rostrata pair is 

 separated by the dry barrier of the Eastern Plains, though they 

 touch, where the climatic conditions approximate, in the Yass- 

 Bowning district. Speaking broadly, the law seems to be cmly 

 of imperfect application to Australian plants. 



