ACACIA SEEDLINGS. 91 



growth in different species, and also even in the same 

 species. As already pointed out in a previous paper in 

 this Journal (1914, p. 136), Acacia rubida may reach a 

 height of ten feet, and bear flowers aud fruit before any 

 phyllodes appear, though it is the only species of phyllo- 

 dineous Acacia so far recorded as doing so, while others, 

 such as A. Dawsoni and aneura, may show considerable 

 transition from petiole to phyllode on the second bipinnate 

 leaf, the succeeding leaf being wholly phyllodineous, and 

 this before the plants are more than two inches high. 

 Others again, such as A. salicina var. varians may show 

 the phyllode almost complete on more than a dozen bipin- 

 nate leaves, before the phyllode appears without any 

 leaflets. 



Development of Uninerves and Flurinerves. 



In studying the transition from linear to dilated petioles 

 and phyllodes, it becomes apparent that in many species of 

 both uninerves and plurinerves one of the first indications 

 of the change is manifested by a thickening of the nerve, 

 partially or wholly, along or near the lower margin of the 

 petiole, with the upper margin sometimes channelled. Next 

 comes a vertical flattening or flange-like extension of the 

 upper margin, with perhaps no dilation for some time on 

 the lower margin, as though the effect of sunlight may be 

 in some way responsible for this curious upward develop- 

 ment. During this development the strong lower marginal 

 nerve may be seen to retain the place of the original petiole, 

 and is continuous from the plant stem to the base of the 

 pinnae. If the phyllode ultimately becomes a uninerve, 

 then succeeding petioles show an increased amount of flange 

 below as well as above the nerve, until at last the phyllodes 

 appear with the nerve in about the centre of the blade, 

 which shows obscurely a system of reticulating veins. 

 (Fig. 3.) 



