Ii8 'Keiajy, Concerning Acacia Phyllodes. [vor\xxix. 



leaf, no matter how unconventional its character, how crude 

 its shape, or how much it differs from our preconceived ideas. 

 For a while it was only an acting leaf — the old one retained for 

 a time a semblance of its old reality, but eventually passed out. 

 The old order changed, and gave place to the new. But was 

 it new ? Once, at least, before it may have been the typical 

 leaf of the genus and have been passed out itself. The 

 ministry had been reconstructed before. How many times, 

 and why these changes ? How did the new form persist ? 

 How is it that now so many distinct forms grow side by side ? 

 The species with bipinnate leaves grow cheek by jowl with 

 species variously phylloded. It cannot be supposed that this 

 was always the case, for then the theory of environment goes 

 by default. Why, then, these changes and the multitude of 

 species ? We must not disregard the world distribution of 

 the genus. It is not exclusively Australian. We cannot 

 altogether fall back on that Mesojiotamia of Australian science 

 — the cataclysm that cut off Australia from the rest of the 

 world. It counts, however, for something. Those that 

 remained on the mainland, spreading latitudinally, developed 

 into the acacias of Africa, whilst the mimosa forms of tropical 

 America either tell of parallel progression or indicate the age 

 of the pinnate type. 



The genesis of Australian species is more than enough to 

 speculate u[)on, and, as they tell their story in cryptic language, 

 imagination must play some part in its interi)rctation. As all 

 the extra-Australian species are pinnate, we can assume, though 

 not with absolute certainty, that this continent contained 

 the pinnate form ever since Australia stood alone. We can 

 also assume that it possessed a phyllode species before Tas- 

 mania was severed from the mainland, seeing that the island 

 State ])ossesses l)oth forms ; and, if we accept the view of the 

 authorities that the change from what they call the normal 

 leaf to the flattened petiole was brought about l)y the struggle 

 of the plant to prevent too rapid transpiration, we can scarcely 

 see that that necessity arose in the mild climate of Tasmania. 

 Both forms, therefore, probably went over with the severance, 

 which phyllodization, therefore, antedates. It is with the last 

 change — the one still in many species incomplete — that I am 

 most immediately concerned. If there were former ones it 

 will suffice for the present that history is repeating itself. We 

 must take ourselves back in imagination to the time when 

 Australia possessed only the normal or i)innate type, in one or 

 more species, established l)y environment from a common 

 parent. 



It would api)ear that Acacia farnesiana is, so far as our 

 knowledge goes, the original acacia from which the various 



