324 



Mr. E. H. Cambage refers to the subject in the following passage : — 



. . . Horizontal and vertical leaves. — The mature foliage of almost all Eucalypts is arranged 

 vertically, and this fact furnishes strong evidence that there must have been considerable development in 

 the genus, for in the great majority of cases the juvenile foliage is arranged horizontally. The same remark 

 in regard to the juvenile foliage applies equally to its nearest allied genus, Angophora. There seems little 

 reason to doubt that the mature foliage also was originally sessile and arranged horizontally, and that the 

 pendant, vertical form is the most recent adarjtation. Throughout the genus Eucalyptus there are various 

 species which show a connecting link amongst their mature foliage, between the horizontal and vertical 

 forms, and in a collection of leaves, some of the foliage may be noticed with the underside pale, which proves 

 the horizontal disposition of the leaf. 



Judging by results, it would seem to have been almost a necessity at some particular stage of 

 Eucalyptus development that some adjustment of leaf arrangement should have been made to conform to 

 some altered climatic condition, and ensure the further progress of the genus. The simplest method for 

 those species to adopt which had already developed petiolate leaves, was to gradually twist the leaf-stalk 

 and so change the position of the blade from horizontal to vertical. It is instructive to inquire intoHhe 

 condition of one or two species which appear to have been unable to do this. (Journ. Roy. Soc. N.S.W., 

 xlvii, 38, 1913.) 



The difference in colour in the juvenile leaves is often associated with thinness, 

 and the leaves contain a high percentage of moisture; they readily curl and dry up, 

 showing their moist environment, and consequent free growth, creating abundance 

 of shade. The question of the pale underside of a juvenile leaf is not entirely a matter 

 of a coastal district, in comparatively rich soil and plenty of moisture, which conditions 

 induce shade by exuberance of foliage. It is frequently seen, irrespective of obviously 

 favourable conditions of soil and moisture, where there is a profusion of seedlings or 

 other juvenile foliage, when the. leaves shelter each other, obscuring the light from one 

 side of a leaf. In some cases, e.g., E. microcorys, the paleness disappears as growth 

 proceeds, but the mature foliage does not markedly differ from the juvenile. 



Shiny. 



Not many leaves can be said to be shiny when they are in the juvenile stage. 

 E. popidi folia is the most noticeable. 



Pale Underside. 



E. globulus and E. Maideni are conspicuous examples of leaves in which the 

 glaucous underside is sharply differentiated from the glabrous upper surface. 



The letter (S) in brackets indicates " Slightly," so far as actually observed. 



E. acmenioides. E. Deanei. 



E. angophoroides. E. diversicolor. 



E. Baileyana. E. Dunnii. 



E. Banhsii (S). E. eximia. 



E. Benthami. E. ficifolia. 



E. botryoides. E. globulus. 



E. cladocalyx. E. goniocalyx. 



E. Cloeziana. E. Guilfoylet. 



E. Consideniana (S). E. Jacksoni. 



