I') 



-radual alteration of the leal venation of the Genus, which commenced with 

 those species closely associated with the Angophoras. Piperitone is usually 

 associated with phellandrene in the oils of species showing this venation, 

 although its occurrence in some of them could not be decided with certainty; 

 hut it is probable that many of the constituents found in these oils are present 

 in traces in many of them. Pinene, also, probably runs through the whole 

 series, of course, diminishing more and more as it is replaced by phellandrene 

 or other terpenes. Phellandrene appears to be present in a maximum amount 

 in the oils of E. dives, E. Andrewsi, E. radiata, &c., and these species show very 

 clearly the characteristic venation for this group. In the lanceolate leaves 

 of these species, too, the marginal vein has receded so far from the edge that 

 often a second one has commenced to form. In the leaves of this group, the 

 reticulations between the more prominent veins in the leaves belonging to the 

 < ineol-pinene group have become still more subordinate, and consequently more 

 room is given for the formation of oil glands, and thus the yields of oil from many 

 species of this group are large. The black dots in the photographs show the 

 position of the innumerable oil glands in the leaves. The reproduction of the 

 venation can be carried out very successfully by photography, the fresh leaves 

 being used. These are printed directly upon the paper in strong sunlight, and 

 the prints thus obtained can be reproduced by any of the well-known 

 photographic methods. 



In October, 1901, we read a paper on this subject before the Royal Society 

 of New South Wales, and demonstrated this alteration of leaf venation in 

 agreement with the chemical constituents, by the aid of a series of lantern slides 

 made from the photographs taken directly from the leaves; the completeness 

 of these can be judged from the reproduction of the leaves in the illustrations 

 (plates I to vm). 



In other parts of this work we show that this alteration in leaf venation 

 and chemical constituents is not local in its incidence, and that the specific 

 characters of each species are practically constant over the whole range of its dis- 

 tribution, and numerous instances are given of this constancy. It can thus be 

 supposed that the formation of the several species of Eucalyptus has been one 

 of evolution, and that the alteration in the chemical constituents of the oil has 

 been contemporaneous with the changing of the leaf venation. It is thus assumed 

 that the several species, as we know them to-day, have gradually deviated from a 

 progenitor, and we have attempted to show through which channels this deviation 

 has taken place. That the constituents of the oil have been fixed and constant 

 for a long period of time must be evident by the fact that, to whatever extent 

 or range any particular species has reached, it contains the same characteristic 

 constituents, and has its botanical characters in agreement. This evidence is 

 of the greatest importance when the length of time is considered which must 

 necessarily have elapsed, before any one species could have established itself 

 over such an extensive area as found to exist to-day. Some Eucalypts, however, 

 appear to possess botanical arid chemical characters which give them an affinity 

 with one or two particular species only, whilst a few seem to have no pronounced 

 connecting features, and, therefore, appear to stand quite alone ; such species are 

 thus not easy to place in a regular line of sequence, as though there were a 

 complete gradation passing from one species to another. The intermediate forms, 

 therefore, seem to be wanting in several instances, which may, perhaps, be largely 

 accounted for by their extinction, or due to mutation. 



The long period of quietude or comparative stability of terrestrial con- 

 ditions in Australia probably accounts for the few indefinite varieties of Eucalypts 

 that we have met with, and the environment also, having undergone little change, 



