Cn. IV] WARM TEMPERATE MOIST SUMMER DISTRICTS 495 



their leaves or the parts performing the functions of leaves being vertical, 

 or presenting their margin, and not either surface, towards the stem ; both 

 surfaces having consequently the same relation to light. This economy, 

 which uniformly takes place in the Acaciae, is in them the result of the 

 vertical direction of the foliaceous footstalk : while in Eucalyptus, where, 

 though very general, it is by 

 no means universal, it pro- 

 ceeds from the twisting of 

 the footstalk of the leaf 1 .' 



Owing to this twisting of 

 the petioles, the crowns of 

 Eucalypti cast only a weak 

 shadow. The connexion be- 

 tween this lie of the leaves 

 and the climatic conditions 

 is evident, and it is not 

 found in young plants of 

 the Eucalypti, or of the 

 Australian phyllode-aca- 

 cias, where the leaves have 

 blades that differ in shape 

 from those of the mature 

 plant, and also place them- 

 selves at right angles to the 

 strongest diffuse light. The 

 leaves of Eucalypti are also 

 markedly xerophilous in 

 structure, and are provided Fi& 2 . g _ Schinopsis Lorentzii) EngL An anacardiace0 us 

 with a thick cuticle, sunken tree of the Argentine thorn-forest (espinal-formation). After 

 i 4.- r Ermler, in Engler und Prantl, Die natiirlichen Pflanzenfamilien. 



stomata, and a coating of H a!f natural size. 

 wax. 



Behr 2 gives of the Eucalyptus-forests of the South Australian mountain- 

 ous districts the following description, which on the whole applies in its 

 leading features to the formation in general : — 



'As a rule, a fairly dense meadow sward, in most cases accompanied by a light 

 park-like forest of gigantic Eucalypti, whose crowns however never meet. The 

 smooth stems, freed from their outer layer of cortex, stand apart at definite and 

 often regular distances. . . . Here and there where the soil is poorer occur Casuari- 

 neae, whose brownish grey crowns in spring-time keenly contrast with the fresh 

 green of the sward. They attain a height of 20 feet, or at least 30 feet, and stand like 

 dwarfs by the side of the Eucalypti. The gum-producing acacias, Acacia retinodes 

 and A. pyenantha, also belong to this vegetation. . . .' 



1 R. Brown, op. cit., p. 62. 2 Behr, op. cit., p. 546. 



