Ii6 Kelly, Concerning Acacia Phyllodes. [v'ol'xxi' 



Nat. 

 X. 



(&) Obsolescent l)iinnnate leaves on the young plant, soon 

 replaced by the broadened or spinescent stalk, with 

 rarely, if ever, a sign of pinnate leaf afterwards : or 



(c) Phyllodes, as on the Blackwood, Acacia melanoxylon, 

 in which vestiges of the pinnate leaves appear at the 

 ends of the broadened petioles for some time during 

 the growth of the tree, and which recur in more or less 

 profusion on wounded boughs, suckers, and parts 

 affected by galls. In the last-mentioned case the 

 pinnate leaves sometimes form concrescent masses, 

 and at other times irregular tufts and branches. 



The following reference is made to the seedling leaves and 

 vestigial pinnate leaves of Acacia salicina in Lubbock on 

 "Flowers, Fruits, and Leaves" (pp. 119-121) : — "In tropical 

 countries some plants, at any rate, fincl the sun too hot for 

 them. In illustration of the present point perhaps the clearest 

 evidence is afforded by some Australian species, essentially the 

 eucalypti and acacias. Here the adaptations which we meet 

 with are directed, not to the courting but to the avoidance 

 of light. The typical leaves of acacias are pinnate, with a 

 number of leaflets. On the other hand, many of the Australian 

 acacias have leaves (or, to speak more correctly, phyllodes) 

 more or less elongated or willow-like. But if we raise them 

 from seed we fmcl, for instance in Acacia salicina (so called 

 from its resemblance to a willow), that the first leaves are 

 pinnate, and differ in nothing from those characteristic of the 

 genus. In the later ones, however, the leaflets are reduced in 

 number, and the leaf-stalk is slightly compressed laterally. 

 The fifth or sixth leaf, perhaps, will have the leaflets reduced 

 to a single pair, and the leaf-stalk still more flattened, while, 

 when the plant is a little older, nothing remains except the 

 flattened petiole. This in shape, as already observed, much 

 resembles a narrow willow leaf, but flattened laterally, so that 

 it carries its edge upwards, and consequently exj)oses as little 

 surface as possible to the overpowering sun. In some species 

 the long and narrow phyllodes carry this still further by 

 hanging downwards, and in such cases they often assume a 

 scimitar-like form. This, I would venture to suggest, may 

 be in consequence of one side being turned outwards, and 

 therefore under more favourable conditions." 



The same writer goes rather far in saying : — " In one \-ery 

 interesting si)ccies, Acacia melanoxylon, the jjlant throughout 

 life ])roduces both forms, and on the same bough may be seen 

 phyllodes interspersed among ordinary i)innate leaves, the 

 respective advantages being, it would ap])car, so equally 

 balanced that sometimes the one, sometimes the other, secures 

 the j)redominance." 



