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essential oils. That selective influences have been active in bringing about these 

 changes is indicated by the fact of territorial selection by the species themselves, 

 and the chemical peculiarities of certain situations and soils have undoubtedly 

 had marked influences upon the location chosen by the young trees, where it 

 would be possible for them to establish themseh-es and flourish — a study which 

 is now receiving much attention under the name of Ecological botany. In 

 New South Wales there are districts where the Callitris do not naturally occur, 

 and this is apparently due to the peculiarities of these localities being unsuited 

 for their natural establishment. Portions of this State known as the " Black 

 Soil P ains " may particularly be mentioned in this connection, and although 

 some of the species approach these districts on al' sides, yet they do not 

 invade them, and to the Callitris they evidently are forbidden fields. 

 The reason for this peculiarit}' is at present little understood, because 

 researches have not extended very far towards solving the problem of the 

 selective peculiarities of plants generally. In the satisfactory unravelling of this 

 question lies the scientitic afforestation of this countrv, because it must certainlv be 

 more judicious and scientifically correct to plant those trees which are most suited 

 bv habit and constitution to the situation and soil required to be utilised, than 

 to deal with the matter in a haphazard wa\', and anv system of artificially supply- 

 ing the necessary constituents to overcome any natural defect would be quite 

 out of the question. The results obtained from the study of the Eucalypts, growing 

 under natitra' conditions in Australia, showed a remarkable constancy in the oil 

 const'tuents of the several species, and i was found during that investigation, 

 that any well-defined species of Eucalyptus would always give practically the 

 same products, not onh' in oil constituents, but in other chemical peculiarities 

 also. Subsequent investigations have added considerably to our knowledge in this 

 direction, and no marked differences in the general character or constituents of 

 the oil distilled from any one species has yet been found, no matter in what part 

 of the country the trees were grown. It might, of course, be feasible to bring 

 about alteration in the chemical constituents of the plant by artificial methods, 

 e.xtending over a sufficiently long period, but under natural conditions such altera- 

 tions as have taken place must have been slow, although eventually succeeding 

 in establishing such marked differences, both in botanical and chemical characters, 

 as has warranted for classification purposes their separation into distinct species. 



It was felt that the importance of this question required extended investiga- 

 tions with other large Australian genera besides the Eucalypts, and for this purpose 

 material of some of the species of Callitris has been obtained from various localities 

 very far apart, and during several years. It will be seen from the results recorded 

 under the several species, particularly C. glauca, that the chemical constituents 

 of the essential oils of the Callitris are remarkably constant when grown under 

 natural conditions, notably their ester content.* The tannins in the barks are 

 also in agreement, so that it is possible by chemical reactions to distinguish the 

 tannin of C. glauca and allied species, from that of C. calcarata and all the 

 specimens we have so far determined, answered to these distinguishing tests. 

 Spreading over such a large extent of territory as do the Callitris, and being all 

 the time subjected to such diverse climatic and other d rect influences as main- 

 tains over such a large continent, it is perhaps surprising that there are 

 .so few well-defined species of Callitris in Australia. 



The constancy of chemical characters found to occur in the several species 

 has thus been of considerable help in deciding the differentiation governing their 



■iiffercnces in the amount of the predominant limoncnc at certain times of the year have been 

 Ignored in thi-> connection, as we know little about tliis peculiarity at present, and it is still the same terpenc. 



