PRESIDENTIAL ADDRESS, 45 



some cases on the smooth-barked boles, as on E. maculosa 

 and rubida. As already pointed out, (see Horizontal and 

 vertical leaves) it is the method commonly availed of by 

 those species whose leaves are sessile and orbicular to 

 ovate ; x and it appears to be a device adopted as a protection 

 against evaporation which may be caused either by the 

 heat of the dry lowlands, or by the winds and intensity of 

 light in a clear atmosphere on the highlands. 



Thick epidermis. — The thickening of the epidermis has 

 already been referred to under "Thick and Thin Leaves." 



Leaf Venation. 



A study of the venation of a series of Eucalyptus leaves 

 discloses the fact that the lateral veins are arranged at all 

 possible angles with the midrib between the limits of about 

 10 to 80 degrees. Attention was first drawn to the botanical 

 and chemical agreement of these venations in a paper read 

 before this Society by Messrs. Baker and Smith in 1901. 

 For convenience of reference, the venation in its relation 

 to the midrib, may be divided into three classes, viz.: — 

 transverse or right angled, oblique or diagonal, and parallel, 

 although none of the veins form quite so much as a right 

 angle with the midrib, nor are any strictly parallel there- 

 with, and the oblique venation may be regarded as that 

 where the lateral veins have a range of about 25 to 65 

 degress with the midrib. 



In the transverse venation the lateral veins are straight, 

 nearly parallel to each other and close together, while the 

 intramarginal vein is close to the edge, and the midrib is 

 thick. 



In the oblique venation the lateral veins are further 

 apart than in the last form, while the intramarginal vein 

 is at some distance from the edge. 



1 H. Deane, m.a., Proc. Linn. Soc. N.S. Wales, Vol. xxv, p. 471, (1900). 



