300 



The opposite leaves are the primitive leaves, and only a few years ago *it was 

 believed that, in the case of a few species, the opposite leaves persisted through life. 

 Gradually this number has been dwindling, till at length only one or two remain, of 

 which we have not found the true adult form, and careful search may find those yet. 

 At the same time, we must not lose sight of the fact that, as regards several species, 

 they seem loth to part from the primitive or juvenile form, the condition being one of 

 retarded heteroblasticity. Indeed, in these cases, the leaves of some species, to all 

 intents and purposes, preserve their opposite or juvenile character throughout life. 



One of the earliest observers who gave attention to the subject was the late 

 Augustus Oldfield, and from his MSS. (circa. 1864), T extract the following passage :■ — 



On the other hand, there are forms which at certain periods of. their growth are so unlike their 

 adult states, and others that in their young states are so like to the young forms of other species which 

 attain their adult condition without any violent transition, that it is equally impossible to assign any reason 

 for the change in the direction of the vital forces, whereby forms (in the former instance) are made to 

 approach, and others (in the latter) to recede from a certain type. 



As an example of the first kind of variations may be cited the genus Eucalyptus, many of whose 

 members in the young state are very different from the adult forms, and as they frequently retain this 

 habit for several years, and,even produce blossoms ere they have attained the adult forms, it has happened 

 that they have been regarded as specifically distinct from their parents, a striking proof of the inadeqvmcy 

 of the methods now employed to discriminate species. As far as my experience goes — and I have carefully 

 studied seventy-five species in their native localities — there is no species of Eucalyptus which is normally 

 fruticose, or that has opposite leaves in the adult stage, so that all those in the latter category which have 

 been recorded by botanists, must be the young states of species, known or unknown. There are but two 

 of the so-called opposite-leaved species known to me that I have failed to connect with their parent forms. 

 In the one, E. Preissii, this character is by no means constant, for towards the summits of the taller plants, 

 the leaves are decidedly alternate. Of the other species, E. pleurocarpa (tetragona), this much can be said, 

 that the squalid habit of the plant conveys the idea that it is not in a stable condition, and of both forms 

 it may be stated that, inhabiting localities subject to periodical conflagrations, caused by the aborigines 

 in their search after food, they suffer more from such conditions than do most of the plants with which 

 they are associated, owing to the great amount of essential oil that pervades every part of them. In fact, 

 out of the vast number of places in which I have found these plants (which are never associated, E. Preissii 

 growing on rocky hills only, while E. pleurocavpa invariably inhabits localities where the soil is composed 

 of sand and clay), I never discovered one in which, among the living plants, there were not the charred 

 stems of dead ones, and these generally taller than the living plants (pp. 399-403). 



I offer some notes on species which at one time were deemed to be isoblastic, 

 but which subsequent observation has shown to be more or less heteroblastic. All are 

 broad-leaved, except E. doratoxylon. referred to at p. 302. 



E. aspera F.v.M. 

 I am not satisfied that alternate leaves have been found in this species. See 

 Part XXXVII, p. 185, Plate 152. 



E. CINEREA F.V.M. 



This species was, when first described, and for many years afterwards, looked 

 upon as an isoblastic species, but I found lanceolate leaves on the species in the Goidburn 

 district, N.S.W. (Proe. Linn. Soc. N.S.W., xxvi, 551, 1901); see also this work, Part 

 XXI, Plate 89. 



