136 HENRY G. SMITH. 
The elastic substance so quickly changing as the leaves 
grow larger, seems to indicate that it is required to act 
solely as a protection in some way to the young shoots. It 
is perhaps a remnant of conditions which maintained ages 
ago, and of which weat this time have no conception. The 
evidence which has accumulated, indicates that Angophora 
is the older genus, and that H. corymbosa is at the end of 
the Kucalypts next to the Angophoras. If the substance 
remained as an entire coating as the leaves grew larger, 
the ordinary functions of the leaf would be interfered with, 
and it was not far down in the sequence of species before 
nature discarded the elastic coating altogether. The 
shoots and young leaves of Eucalyptus species growing 
together with EK. corymbosa gave no indications of the 
elastic substance by ordinary physical methods, although 
their young shoots were just as pronounced, and often quite 
asred. EH. pilularis, E. hcoemastoma, E. eugenoides and 
E, botryoides all gave negative results in this respect. 
It hardly appears possible that the coating is reserve 
material to be used in the formation of the leaf, and the . 
yield of essential oil from both E. corymbosa and A. lan- 
ceolata is so very small, that it is hardly likely to be used 
in the formation of oil constituents; it most probably 
undergoes oxidation, ultimately forming the powdery sub- 
stance, with perhaps a little wax at the same time. That 
the alteration is in this direction is demonstrated by treat- 
ing the older leaves with ether for three minutes, the white 
powdery substance being thus removed. From the method 
of extraction it must be on the surface of the leaf. 
The following evidence obtained by treating the shoots 
and leaves separately supports this theory of alteration. 
The accompanying photograph, which is that of the end of 
one of the growing branchlets of E. corymbosa, gathered 
April 11th 1908, will assist in making this clear :— 
