BOTANICAL AND CHEMICAL CHARACTERS OP EUCALYPTS, 113 



development of the genus there has been a reduction in size of the 

 cotyledons, so that the tender germinating seedhng may better cope 

 with the dry conditions of Austraha. This has taken place in some 

 species by a simple reduction in size, in others by a reduction in size 

 and the introduction of emargination. As the alteration in the cotyle- 

 dons has taken place, a more or less corresponding change in the size 

 and shape of the fruits has been effected. Lastly, the morphological 

 characters of the cotyledons and primary leaves are constant in each 

 species. The variation that takes place is more of the nature of a 

 deviation or fluctuating variation. 



The accompanying Plate VI. gives examples of Eucalyptus 

 cotyledons — natural size. 



Notes on the Evolution of the Oenns Eucalyptus. By E. C. Andrews. 



Risume. — Eucalyptus is a highly specialised or secondary form 

 of the pi'imary or fleshy-fruited Myrtaceae. The primary types are 

 luxuriant and occur throughout the fertile tropics, whilst Eucalyptus 

 and its allied genera are adaptations, in the main, to the more barren 

 sandy and extra-tropical areas in Australia. Eucalyptus developed 

 in warmer Australia and has never wandered beyond the neighbouring 

 islands of tliat continent, except as a colonist. 



Deane suggests (25) that the capsular-fruited Myrtacese originated 

 in Northern or North-Eastern Australia ; that these types attained their 

 maximum development in Western Australia and gave rise to the 

 fleshy-fruited Myrtacese, which spread later to Asia and Europe as 

 differentiations of the primitive capsular type. Deane's idea 

 apparently arose from the belief that capsular fruits had been developed 

 before the fleshy forms. Even, however, if it be agreed that the 

 capsular preceded the first baccate or drupaceous form of fruit, it does 

 not at all follow that the capsular must precede the fleshy fruits in any 

 particular family, especially such a relatively young one as the 

 Myrtacese. 



In connection with the position of the subject genus in its family 

 it may be pointed out, in the first place, that the' family Myrtaceae 

 consists of about 3,100 species, of which 2,500, approximately, occur 

 in the fertile tropics or subtropics of the whole world. These include 

 the vast genera Eugenia (1,325 species), Myrtus (200 species) and 

 Myrcia (320 species) ; they are all of luxuriant habit, including some 

 of the finest trees in the jungle. Eugenia and Myrtus are rich in 

 species in America, Asia, Africa but occur more sparingly in Australia. 

 All possess fleshy fruits, whereas Eucalyptus is a capsular form. Again, 

 these fertile tropical types all possess leaves which are opposite and 

 penniveined, dense, glossy and luxuriant in appearance. The anthers 

 of all, moreover, are versatile, the cells parallel and opening longi- 

 tudinally. 



On the other hand, Eucalyptus possesses various forms of anthers ; 

 nevertheless, those of the section Corymbosae or the ' Bloodwoods ' 

 exhibit the generalised type which is found in the tribe of the Myrtse 

 or the fleshy-fruited forms of the familv. Moreover, it is just the 



1015. ■ ; 



