BOTANICAL AND CHEMICAL CHARACTERS OP EUCALYPTS. 107 



interior, west of the Main Divide, in I'esponse to this change, have 

 gradually been adapted to the new conditions, the result being that they 

 differ considerably from many of the coastal species and most of 

 all from those on the higher mountains. None of the Eiicalypts of the 

 interior occur in Tasmania. 



The Eucalypts belong to a family whose leaves are normally opposite 

 and hoi'izontal; they are also closely allied to the genus Angophora. 

 The ' Bloodwood ' group of Eucalypts show the greatest resemblance to 

 the Angophoras, both as regards leaves and oil contents; they may, 

 therefore, be regarded as representing the type of the oldest Eucalypts 

 now living. They grow in sandy soil and avoid the cold. Apparently, 

 the early Eucalypts flourished in a sandy soil with a warm climate, 

 probably in Northern Australia. The bark was scaly to rough ; the 

 leaves were opposite and horizontal and often covered with stellate 

 hairs (22) or coated with caoutchouc ; the leaf-venation was transverse, 

 the numerous lateral veins forming an angle of upwards of about 65° 

 with the midrib ; the flowers were generally large as compared with 

 those of the genus at the present day and possessed, anthers which 

 opened longitudinally in parallel slits (Parallelantherse) ; the fruits were 

 generally larger than those of the more recent species of to-day ; the 

 chief constituent of the essential oils contained in the leaves was 

 pinene (5). Following some alteration in environment, partly climatic 

 and partly through the advent of more basic soils resulting from volcanic 

 outpourings, a new development took place in the genus and species 

 were evolved with various kinds of bark (hard-furrowed, fibrous, or 

 smooth barks). The mature leaves, which now showed a more oblique 

 or diagonal venation and were alternate, had gradually developed 

 petioles, which allowed them to hang vertically, so as to present the 

 least possible surface to tlie sun and thus minimise transpiration, whilst 

 those which remained sessile became protected with a glaucous powdery 

 wax or a thickened epidermis. Some species of this new type — the 

 ' Box ' trees amongst others, many of which flourish on the more basic 

 soils — possessed anthers which opened in terminal pores (porantherse), 

 and cineol now became an important constituent of the essential oils. 

 As the genus encountered colder conditions, partly through spreading 

 southwards and partly through ascending the mountains which were 

 uplifted in Eastern Australia towards the close of the Tertiary period, a 

 fui'ther group was evolved having leaves with almost parallel venation 

 or with the now much reduced number of lateral veins at an angle of 

 less than about 25 degrees with the midrib, kidney-shaped anthers with 

 the cells divergent at the base and confluent at the summit (Renan- 

 therse) ; the essential oils in the leaves contained much phellandrene 

 and little, if any, pinene. This group is largely represented by the 

 ' Peppemiint ' trees. On comparing seedling and adult foliage, 

 evidence of transition in leaf form is found in nearly all species ; in 

 the cooler country types, such as E. coriacea and E. stellulata, the 

 lateral veins of the seedling foliage are arranged at angles up to 50 

 degrees with the midrib, whilst in, mature leaves the angles are less than 

 10 degrees and in most cases the veins ai'e practically parallel with 

 the midrib. 



