

Hybridisation. 



["his verj fascinating question I ntion oi modem botanists 



to some extent, and we also have given iough1 to the subject, bu1 



so far without any measure of success. On seriously following up the identity 

 of supposed Eucalyptus hybrids, in several ca ation thai these w< 



th<' offspring oi certain indicated parents, has been found to be withoul solid 

 support. 



Natural hybridisation in the Eucalypts perhaps, appeals i ie as .1 



xplanation for the estabhshmenl oi certain species which show affinities 

 mi both sides. The organs oi reproduction in Eu< alj ptus, however, are protected 

 by an operculum, and in many cases pollen grains are found adhering to the 

 stigma before the operculum falls off, so that it may be just .1- readilj supposed 

 thai the cap in the bud is a protection against hybridisation. 



Baron von Mueller at one time did not regard hybridisation as impossible, 

 but thou- lu that .ill ordinary chances are against it, for he states : ' Hybridisa 

 tion does not seem to explain the origin oi these aberrant forms in a genus, 

 where cross-fertilisation is guarded by a calycine lid." (Eucalyptographia, 8th 

 1 >ec, under E. cordata.) 



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

 really distinct species, and in our opinion cross-fertilisation in the Eucalypts 

 under natural conditions is quite exceptional, especially when we know that 

 numerous -prut- are growing intermixed, often flowering at thi . tim and 

 undei supposed favourable conditions for hybridisation, yet preserving 

 throughout extensive areas their specific characters with remarkable constancy. 



We were very much impressed with this aspecl oj the question on the 

 completion of our work on the Eucalypts of Tasmania, and ii was striking to 

 find such a large percentage oi the species (quite half) oi those now growing in 

 [Tasmania, which are identical, both botanicallj and chemically, with the same 

 Eucalypts growing on the mainland oi Australia. Ii is thus evident that these 

 species war well established in both Australia and Tasmania before the latter 



was separated from the conti t, and thai in both localities they have gone on 



reproducing their offspring in absolute constancy ever since. It is thought th; 

 ii was not earlier than tertiary times when Bass Strait was formed, and 

 although this period is perhaps nol far back geologically, yet, considered 

 botanically, it must have been a verj long time ago; but, through all this period 

 "l time only a very few species oi Eucalypts have become endemic in Tasmania. 

 Ii may be mentioned that since our work on the Tasmanian Eucalypts was 

 completed, E. acervula, which was considered as endemic in Tasmania, lias also 

 been found growing in South Australia; and possibly when the Eucalypts on 

 the Australian Alps shall be mor< completely studied, other Tasmanian species 

 will be found to exisl on the main! How very different this condition 



oi affairs musl have been it hybridisation wei »mmon occurrence with the 



Eucalypts. Ii is thus evidenl thai very definite knowledge is needed before 

 one can ao tatement that such uch a Eucalyptus tree is a hybrid 



uudei na 1 ural conditions. 



