82 R. H. CAMBAGE. 



the Indian Archipelago, and the Pacific Islands, and these 

 closely resemble some of the species of tropical Australia. 1 



Sequence in the Development of Leaves. 



As already pointed out, the usual sequence in the develop- 

 ment of the leaves is that the cotyledons are succeeded by 

 one simply-pinnate leaf, and this is followed by a varying 

 number of alternate abruptly bipinnate leaves, the common 

 petioles being mere stalks on the lower leaves, but gradu- 

 ally becoming more dilated on the upper ones, until at last 

 they develop without any bipinnate leaves on their tips, 

 and carry on the functions of ordinary leaves. 2 



From an examination of about 400 seedlings of about 60 

 species, the above sequence is found to be maintained in 

 the great majority of cases, in fact only four species have 

 been noticed so far, which show a constant divergence. 

 The point of difference lies in the number of simply-pinnate 

 leaves. Seedlings of the majority of species so far examined 

 have only one pinnate leaf, immediately following the 

 cotyledons, but in four species, about 70 examples have 

 been found to produce an opposite pair of pinnate leaves. 

 One seedling of A. aneura had an opposite pair of pinnate 

 leaves, though this species appears to commonly have only 

 one. In every case this pair has been succeeded by a 

 bipinnate leaf, and except for the pinnate leaves appearing 

 singly or in pairs, the sequence is the same in each case. 

 In no instance has an example been found with the cotyle- 

 dons immediately succeeded by a bipinnate leaf, although 

 Lubbock records Acacia Burkittii as such a case. 



1 B. Fl., Vol. ii, p. 301. 



8 "A Contribution to our Knowledge of Seedlings," by Sir John Lubbock, 

 Vol. i, p. 339, (1892). 



" Dimorphic Foliage of Acacia rubida&nd Frutification during Bipinnate 

 Stage/' by E. H. Cambage, this Journal, xlviii, p. 136, (1914). 



