66 



Of course, the opening of the flower serves some purpose in nature, and no doubt insects and other 

 agencies assist or contribute in cross-fertilisation in very rare cases, but in such instances the possible 

 sterility of these hybrids must be taken into consideration. 



Cross-fertibsation in the case of eucalypts is, in our opinion, quite exceptional, especially when 

 we know at this present time that millions of these trees are growing intermixed, and although often 

 flowering at the same time, yet preserve throughout extensive ranges their specific characters with 

 remarkable constancy. 



Maiden, 1903, 1904. — I have already referred to my papers on hybridisation 

 under these dates. 



See also my paper " Further Notes on Hybridisation in the genus Eucalyptus " 

 (Proc. Linn. Soc, N.S.W., xxx, 492, 1905) which contains specific instances attributed 

 to this phenomenon, also " On a Eucalypt Hybrid (E. calo-phylla x E. ficifolia)," (ib. 

 xli, 185, 1916). I have published other brief notes on hybridism in the present and 

 other works. 



Hall, 1912 — 



In considering the question of hybridisation between Eucalypts, full consideration should always 

 be given to the time of the year at which they flower. Thus, crossing of E. robusta, which blooms in 

 winter, with E. hemiphloia, which is out in summer, would be impossible, though there is a chance of such 

 crossing occurring between E. tereticornis and E. paniculata, or E. saligna and E. acmenioides. But the 

 mere fact of two species growing together and flowering at the same time, yet maintaining constant and 

 specific characteristics over a great range, points to the conclusion that hybridisation is most unbkely or 

 impossible between them. In fact, I think the law may be laid down, that natural hybridisation is 

 unlikely to occur between two species growing freely together and flowering at the same time. If I were 

 attempting to hybridise Eucalypts, I should expect greater chances of success from two species growing 

 widely apart, as say from Western and Eastern Australia, than from two growing together and 

 blooming simultaneously. (Cuthbert Hall, Proc. Linn. Soc. N.S.W., xxxvii, 566, 1912.) 



See also Dr. Trabut's remarks, written in 1904, quoted at p. 73, below. 



Hall, 1914 — 



Again as to hybridism, I have been keenly on the alert to discover instances of this, but, after 

 examining thousands of seedlings from different species, I have not seen one single instance pf it so far. 

 Although the seedbngs of many species differ so markedly from one another, that they could be detected 

 at once, I have hitherto found them uniform throughout, though there may be slight differences in size, 

 vigour, &c. Still, knowing that hybridism has actually been proved in the genus Acacia (Proc. Linn. Soc. 

 N.S.W., xxxv, Part II), of which, as of the Eucalypts, so many species occur in Australia, we may hope 

 soon for actual demonstration of such occurring in the latter. Up to the present, though much has been 

 said as to one species being a hybrid of two others, we have had no actual proof. (Cuthbert Hall, Proc. 

 Linn. Soc. N.S.W., xxxix, 475, 1914.) 



At the same time Dr. Hall, in his description of E. Marsdeni (Proc. Linn. Soc. 

 N.S.W., xliii, 747, 1918) shows that he does not exclude the role of hybridisation in 

 the genus. 



Maiden, 1914. — I give copy of an extract ("Hybridism in the Genus") from 

 a paper I read before the British Association for the Advancement of Science at its 

 Sydney meeting in August, 1914, and a paper by Mr. Cambage and myself entitled 

 " Observations on some reputed Natural Eucalyptus Hybrids " (Journ. Roy. Soc. N.S.W., 

 xlviii, 415, 1914), may be turned to. 



