110 REPORTS ON THE STATE OF SCIENCE. — 1915. 



the cotyledons are of great importance in the differentiation of species. 

 Tlie form and size are constant in each species and do not varj% except 

 within narrow hmits which may rather be termed fluctuations. 

 Lubbock says that the cotyledons of most species are entire. In the 

 Eucalypts the emarginate form is the more common. Hence we get 

 two great classes, the entire and the emarginate. the fomier being the 

 more primitive type. In the size of the cotyledons, the species differ 

 greatly, at one end of the scale being the exceedingly large ones of 

 E. calophylla, E.Br, and about 25 cm. broad, at the other the very 

 small ones of E. acacia for mis, 0'2 cm. broad. The original Eucalypts, 

 represented now by those of the E. corymbosa class, had large entire 

 reniform cotyledons ; these are practically identical with those of the 

 nearly related genus Angophora. The evidence of the seedlings thus 

 bears out the chemical and morphological evidence as to the near 

 relationship of the two genera. The group of ' Stringybarks,' repre- 

 sented in E. obJiqua and its allies, also have seedlings with entire 

 reniform cotyledons ; these are usually much smaller than those of the 

 preceding group. But the interesting fact is to be noted that whilst 

 the members of the corj'mbosa group elaborate an oil of e. simpler com- 

 position, resembling the oil found in the Angophoras, its principal 

 constituent being pineue, in the case of the ' Stringybarks ' some species, 

 such as E. IcBVopinea and E. dextropinea. afford a pinene oil, whilst 

 E. eugenioides yields a pinene-ciueol oil, E. macrorrhyncha, E. 

 capitellata and E. nigra a pinene-cineol-phellandrene oil and E. obliqua 

 a phellandrene-aromadendral oil. It will thus be seen that whilst the 

 bark, anthers (all these have reniform anthers as compared with the 

 parallel anthers of the corymbosae) and cotyledons have remained stable, 

 a great evolutionary change has occurred in the oils. Whether hybridisa- 

 tion has played a part in this we cannot as yet saJ^ 



Among the entire cotyledons, there is yet another small group 

 consisting of species with small circular or reniform cotyledons. These 

 are probably derived from an ancestor in which emargination was 

 present but in the process of reduction in size this has been lost. The 

 fact that they all give a cineol oil also points to such a conclusion. 



Of great interest is the important class of Eucalypts with emarginate 

 cotyledons. Whether we have any of the species in which this 

 emargination first appeared, it is hard to say ; but this much is probable, 

 that, until it appeared, the Eucalypts were unable to migrate from the 

 warm moist coastal ai'eas to the dry interior, to grow on any but a 

 sandstone formation or to elaborate any but a simple oil not containing 

 cineol. One of the first steps in the evolutionary development of the 

 Eucalypts, whereby they became adapted to all the vicissitudes of 

 Australian physical conditions, has been the development and improve- 

 ment of the emarginate cotyledons. It is probable that the change first 

 took place in some such species as E. marginata, Sm., of Western 

 Australia; this has a large cotyledon with well-marked emargination 

 but the oil is of the simpler pinene type. This group is not large and 

 evidently the large emarginate cotyledon type could not exist away 

 from the moist coastal region any more than the large entire cotyledon 

 type. I am not aware of the character of the soil in which the members 



