162 THE INSTABILITY OP LEAF-MORPHOLOGY, 



phila A. Cunn., showing gradations from flat to cylindrical, 

 under varying climatic conditions. The influence of xerophytic 

 or hygrophytic conditions on leaf- variation was illustrated by a 

 series of examples, e.xhibited before this 8ociety(13; 1915, p.418), 

 of Bossicea heterophylla Vent., (a species whose foliar instability 

 is intimated by its specific name) in which the transition from a 

 degree of aphylly, in the elevated, dry- ridge xerophyte, and 

 harsh, diminutive foliage of its fellow of the dry claypan, to the 

 broad, soft leaves of plants of this species living under hygro- 

 phytic conditions, was demonstrated; in these latter examples, 

 to which under normal conditions a regular supply of water is 

 assured, the flattened stems, and the persistence of the narrow, 

 linear leaves in company with the broader ones (heterophylly), 

 disclose a provision for a return, when necessary, to xerophytic 

 conditions, as it was noted that the broad leaves exhibit extreme 

 sensitiveness to drought-conditions, and respond by becoming 

 deciduous. A series of specimens of Platylohium formosum 8ra., 

 exhibited before this Society (13; 1915, p. 4 15) showed alterations 

 in the size of leaf brought about by xerophytic versus hvf'ro- 

 phytic conditions. It is noted tliat several genera of Western 

 Australian Leguminosai are exceptionally liable to marginal leaf- 

 variation. 



« 



Saxifrages. 



The alternation of seasons favourable or deterrent to plant- 

 growth, has caused considerable leaf-variation in Ceratopetalum 

 gihitimiferum Sm. In some examples from Cowan (Cull. A. A. 

 Hamilton; May, 1915), the larger leaves are found on the tips 

 of the branches; in others, the smaller leaves are so placed, and 

 there is a third stage showing a branch on which the leaves are 

 all small, and closely packed. 



Droseuaces. 



The leaves of Drosera peltnta Sm., and D. anriculata Backh., 

 are identical, and those of some of the rosetted forms are barely 

 separable. 



