TRANSACTIONS OF SECTION K. 5&3 
leaves was pinene. With some alteration in environment, partly climatic and 
partly through the advent of more basic soils resulting from volcanic out- 
pourings, a new development took place in the genus, and species were evolved 
with hard furrowed, fibrous or smooth barks. The mature leaves, which now 
showed a more oblique or diagonal venation, and were alternate, had gradually 
developed petioles, which allowed them to hang vertically, so as to present the 
least possible surface to the sun and thus minimise transpiration, while those 
which remained sessile protected themselves with a glaucous powdery wax or 
with a thickened epidermis. Some species of this new type possessed anthers 
which opened in terminal pores, while cineol became an important constituent of 
the essential oils. As the genus encountered colder conditions, partly through 
spreading southwards and partly through ascending the mountains which were 
uplifted in Eastern Australia towards the close of the Tertiary, a further 
group was evolved having leaves with almost parallel venation, or the lateral 
veins now much reduced in number, at an angle of less than about 25 degrees 
with the midrib, kidney-shaped anthers with the cells divergent at the base 
and confluent at the summit, and essential oils in the leaves containing much 
phellandrene, and little, or in some cases no pinene. By a comparison of 
seedling and mature foliage, evidence of transition in leaf form is found in 
nearly all species, and in the cold-country types, such as Hucalyptus coriacea and 
H. stellulata, the lateral veins of seedling foliage are arranged at angles up to 
50 degrees with the midrib, while in mature leaves the angles are less than 
10 degrees, and in most cases the veins are practically parallel with the midrib. 
Eucalyptus leaves with transverse venation are absent from Tasmania, are con- 
fined to a very small portion of North-eastern Victoria and practically 
below the 3,000-foot level in New South Wales, but are common on siliceous 
soils in Northern Australia, thus showing a preference for the warmer climate. 
Eucalyptus leaves with parallel venation occur in Tasmania, Victoria, and 
Bastern New South Wales, while in Northern New South Wales their home is 
above the 3,000-foot level; and they are absent from Northern and Western 
Australia, but are found at the highest point that any Eucalyptus grows in 
Australia, viz., 6,500 feet, thus showing a preference for cold and moist 
conditions. 
4. Variation and Adaplation in the Eucalypts. 
By Dr. Curuspertr Hatn. 
Eucalypts have always been credited with an excessive tendency to varia- 
tion. However, many of the so-called variations should more properly have the 
terms deviations or fluctuation variations of De Vries applied to them. These, 
are responses to physical conditions to which the genus is particularly sensitive. 
Apart from these deviations there are many instances where two or more forms 
closely approach each other. Some of these which were classed as varieties 
should now, in the light of fuller knowledge, be counted as distinct species. 
It is wiser to give specific rank wherever possible. Evolution and the pro- 
duction of variations seem to be still actively going on amongst the Eucalypts. 
Instances of variations may be given, among which is one I shall shortly 
describe—evidence of the cotyledon leaves as to variation and adaptation. In 
the 1. corymbosa group these closely resemble those of the Angophore. 
Emargination has had a great influence on the evolution of the cotyledons and 
their adaptation to Australian conditions. This has gone on coincidentally with 
the evolution of other morphological characters and of the essential oils. 
TUESDAY, AUGUST 2%. 
Joint Discussion with Sections C (Geology), D (Zoology), and 
E (Geography) on Past and Present Relations of Antarctica in their 
Geological, Biological, and Geographical Aspects.-—See p. 409. 
