218 A CONTEIBUTION TO, ETC. 



the particular group under which each species should be ranged, 

 the basis of the system is likely to be permanent. As regards 

 the fixing of species, and of ascertaining the amount of variation 

 to which some are liable, other principles must be applied. 

 Some species, indeed, are marked by the double operculum, some 

 by winged seeds, and others by the colour of their stamens ; but 

 the shape, cells, valves, &c., of the seed vessels present very 

 important notes of distinction, and deserve the most attentive 

 study. Hence I believe that these considerations, when taken in 

 connection with the cortical group to which the respective species 

 belong, will be found most efficacious in settling many difficulties. 

 It is true, indeed, that some seed \essels of very different trees 

 closely resemble each other, and, consequently, without some 

 further mark for distinction, mistakes might arise ; but the diffi- 

 culty is considerably lessened when the group of the tree from 

 which the specimen was procured, is known. For instance, some 

 species of the Leiophloia have seed vessels very similar to those 

 of the Pacliypliloice ; and if a person did not know to which 

 group they belonged, he might probably err in referring them to 

 the wrong species. This, however, is not so likely to be the case, 

 when he can ascertain whether they were collected from a tree 

 with smooth bark, or from one with fibrous bark. It seems to me 

 that a system founded on the character of the seed-vessel in con- 

 nection with the bark, will ultimately fix the species of the genus, 

 for generally speaking the fruit is subject to the least variation. 

 Even in the grey gum or hybrid box (E. tereticornis) , which 

 appears more subject to variation than any gum in New South 

 Wales, there is sufficient uniformity in the seed-vessel to mark 

 the species. The leaves are subject to great diversity, for they 

 may be found of all shapes and sizes from broad ovate to narrow 

 lanceolate ; and the umbels (though the type is apparently of 

 seven flowers on each umbel), vary considerably in number, 

 whilst the operculurn, which is usually much longer than the 

 cupula, is sometimes equal in length to it, and sometimes shorter. 

 But after all, if the seed vessel be considered in reference to the 

 bark of the tree to which it belongs, it will be a safe guide to the 

 determination of the species. It is in this gum that workmen 

 speak so much of hybridization, as they imagine that the flowers 

 of the grey gum are sometimes inoculated by the pollen of the 



