TERPENOIDS 



237 



A communication from another worker concerning the mor- 

 phology of these plants is quoted by Penfield and Morrison: 



I tried every point to see if there is any morphological difference be- 

 tween these two forms, but failed to find one single character to distin- 

 guish these two trees. . . . Seedlings, young and matured foliage, buds 

 and fruits, all agree with the other. I spent many hours over this 

 examination that I might not miss any point." 



According to Penfield and Morrison, E. dives is thought to be 

 a hybrid. Thus they feel that such oil variation "seems only reason- 

 able." Yet, why is there so httle evidence in a hybrid of morphological 

 variations? The fact that so much effort and attention was devoted 

 to the question of whether the chemical forms of E. dives could 

 be otherwise distinguished is indicative of the influence that the earlier 

 phytochemical work had with respect to the question of chemical 

 constancy within a species. 



Baker and Smith did not apparently consider hybridization 

 to be an important factor in the evolution of Eucalyptus. 



It may be now shown that most of these supposed aberrant forms are 

 really distinct species, and in our opinion cross fertilization in the 

 Eucalypts under natural conditions is quite exceptional, especially 

 when we know that numerous species are growing intermixed, often 

 flowering at the same time, and so under supposed favourable condi- 

 tions for hybridization, yet preserving throughout extensive areas their 

 specific characters with remarkable constancy. 



Four types of E. dives were subsequently recognized, all based 

 on oil character differences: 



E. dives, type 



piperitone, 40 to 50 per cent; phellandrene, 40 per cent 

 E. dives, var. A 



piperitone, 5 to 15 per cent; phellandrene, 60 to 80 per 



cent; piperitol (small amount). 

 E. dives, var. B. 



piperitone, 10 to 20 per cent; cineole, 25 to 50 per cent; 



together with phellandrene 

 E. dives, var. C. 



Cineole, 45 to 75 per cent; piperitone, under 5 per cent; 



phellandrene, absent, or present in small quantity only. 



Although Baker and Smith considered that oil characters did 

 not usually vary greatly within a species, they found examples 



