BV A. A. HAMILTON. 153 



references from the works of Australian botanists, illustrating 

 the leaf-characters affected, is now submitted, and, in certain 

 cases, evidence is offered as to the conditions operating in the 

 production of leaf-variation. For exotic examples and more 

 detailed causation, see Schimper(23) and Warming(25) The 

 factors affecting leaf-morphology, examples of which are given, 

 may be briefly summarised. 



Edaphic. — 'J'he preference shown by certain plant-associations 

 of our indigenous flora for a particular soil-formation has been 

 demonstrated by local botanists and geologists (though further 

 data on this interesting subject are desirable), and this influence 

 is largely contributory to leaf -variation: the growth on a rich 

 basaltic soil, compared with that inhabiting a poor sandstone 

 formation, needs no comment, so obvious is the effect on the size 

 and shape of the leaves in plants capable of adaption to both 

 situations. 



Climatic. — The degree of heat or cold encountered largely 

 regulates the size, pilosity, texture, and glaucousness of leaves. 

 The occurrence of similar forms of leaf in some species of alpine 

 and desert plants, due to the climatic conditions obtaining in 

 such regions, is noted in all ecological text-books; and plants 

 approaching these inhospitable regions from stations in which 

 the conditions are more temperate, exhibit variation, which, in 

 some instances, may be traced by well marked gradations. 



Exposure v. Shelter. — The adaptable, dry ridge, or elevated 

 plateau habitue, alters its foliar characters in cojiformity with 

 the conditions obtaining in the valley, or sheltered slope, when 

 changing its habitat. The close association of plants (growing 

 in exposed situations) for mutual protection and shelter, modifies 

 the size of the leaf. 



Elevation. — The measure of elevation is seen to affect leaves 

 in size, pilosity, and texture. Examples of hairiness in alpine 

 plants growing under xerophytic conditions, and glabrous forms 

 growing as hygrophytes are givendS; p 34). 



Phenological. — Irregularity of rainfall is the principal agent in 

 phenological leaf -change; a sudden, copious rain after a prolonged 

 period of drought, accelerates the production of foliage which 



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