PRESIDENTIAL ADDRESS. 19 
were thus more completely indicated, and the contempor- 
aneous alterations, both in botanical features and chemical 
constituents, could thus be followed throughout the series. 
In the foliage of Callitris spp. the secretion of essential 
oil takes place in one or more pockets hidden in the summit 
towards the free ends of the adnate decurrent leaves, and 
in the numerous sections observed the secretion glands 
show no passage to the outer air. It thus appears that 
with the Callitris there is no exhalation of the essential 
oil product, this apparently being utilised by the plant in 
other ways. Although the oil constituents vary consider- 
ably in the various species, yet, these are comparatively 
constant for each, and it does not matter how extensive is 
their natural geographical distribution the results are the 
game. The yield of oil for each species is also fairly con- 
stant, indicating also a uniformity insecretion. The form- 
ation of the alcohols borneol and geraniol in the oils of the 
Callitris is also in a uniform direction. In those species 
which, perhaps, constitute the oldest members of the genus 
now living in Australia, the greater portion of the ester 
consists of bornyl-acetate, but as the genus evolved, the 
latter ester increased in amount until in the oils of certain 
species growing on the extreme eastern portion of the 
continent, and in Tasmania, it had entirely supplanted the 
bornyl-acetate, and at the same time had increased in per- 
centage amount. By analysis it was possible to follow the 
diminution of the one ester, and the corresponding increase 
of the other, and also to show that when the bornyl-acetate 
had been quite supplanted that the free alcohol was entirely 
geraniol. As the chemical characters changed the botanical 
features altered in agreement. 
The comparative constancy of individual species, in both 
botanical and chemical directions, is so definite that there 
is little fear that subsequent investigations will upset con- 
