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classification. Not only has it been possible by this method of investigation to 

 indicate the possible economics belonging to the several well-defined species, but 

 at the same time to correlate the differences of alteration in the species them- 

 selves, and so allot spec' fie values to those botanical characters which evidently 

 have been established under exactly similar conditions and influences as those 

 which fixed their chemical differences. The determination of the possible changes 

 which may be brought about by specific treatment of the several species must be 

 left to other investigators. In this work, only those plants established under 

 natural conditions have been dealt with, and the results which have thus far been 

 obtained with these, do not warrant the supposition that alterations are now 

 taking place with sufficient rapidity to enable one to discern them. Evidently 

 time is one of the main factors in these alterations, and human life is too short 

 for their discernment. Results having been obtained from nearly the whole of 

 the genus Callitris, gathered throughout the whole range of its distribution, it 

 has been possible to formulate conclusions, which could not have been advanced 

 if the study had been restricted to any one species. 



In both Callitris and Eucalyptus the leaves are persistent during the whole 

 year, and the flowering period seems to play a comparatively small part in the 

 chemical changes of the essential oils in both genera, so that the results which have 

 been obtained in Europe, by the study of those chemical changes which take 

 place in the oils of such plants as Mentha piperita, Pelargonium odoratissimum, &c., 

 during their several periods of growth and flowering, appear scarcely to assist 

 when applied to such genera as Callitris and Eucalyptus. The changes which 

 occur in the oils of these plants seem to be specific, and no periodic alterations 

 of a very marked character have been found in any one well-defined species, so 

 that only slight differences in the constitution of the essential oils are perceptible 

 during any part of the year. Supposed differences in this direction have often 

 been found to be due more to differences of opinion as regards nomenclature, than 

 to the alterations in the constituents of the specific species themselves. It is thus 

 seen that the chemical products manufactured by individual species, both in 

 Callitris and Eitcalyptus , have a considerable systematic value, and their study, 

 therefore, becomes of some importance when seeking for specific differences in 

 plant classification. 



The conditions — largely of a chemical nature — which succeeded in establish- 

 ing such definite alterations, also brought about marked differentiations in the 

 character of the species themselves. This conclusion may be supported by such 

 well-defined species as Callitris glauca, and C. calcarata, the former growing almost 

 exclusively on the plains, the latter species on the hills. In districts where both 

 occur it is possible to roughly follow the margin of the location of either species 

 on the map, and at the same time indicate fairly well the contour of the hilly 

 country. Wherever C. glauca occurs, its chemical peculiarities are found to be 

 specific in all directions, and markedly so in contradistinction with those of 

 C. calcarata, or vice versa. It seems necessary, therefore, that the conditions which 

 were originally responsible for the establishment of these characteristic chemical 

 peculiarities should persist, if the results are to be of a permanent nature. It is 

 thus reasonable to consider that the well-defined chemical constituents of the 

 plant are, for all practical purposes, as systematically valuable as the morphological 

 characters, and that, when all this evidence is correlated, the species so founded 

 will be established with a considerable degree of stability. C. Tasmanica, growing 

 in Tasmania, gave an oil which agreed entirely with that from the same species 

 growing on the highlands of New South Wales, hundreds of miles away. Evidentlv 

 here the natural conditions under which the species had become established were 



