PRESIDENTIAL ADDRESS. 29 
by the community. Day by day the pest is extending, and 
year by year the millions of acres already infested are being 
added to by hundreds and thousands. With a problem of 
this nature, it is highly improbable that any royal road 
to eradication will be discovered. The Experiments Super- 
vision Committee of the Department of Agriculture is 
actively engaged in investigating the most effective means 
of destroying the pear, and has in hand experiments to 
test the relative costs of the different methods suggested. 
These comprise mechanical means and spraying with cer- 
tain preparations of arsenic. All are costly, and in poor 
country the expenses of eradication will often exceed the 
value of the land. The fact that Opuntia monocantha, a 
pest pear in parts of Australia, can be destroyed by the 
cochineal insect, suggests the possibility that a mutant 
from it may possibly be found which would attack also 
the common pest pear, O. mermis. Provided there is no 
mechanical reason why these insects cannot feed on the 
latter, massed feeding experiments might be tried on an 
area where the two species are growing together. The fre- 
quent transmission of millions of coccids from plants of 
O. monocantha to adjacent ones of O. inermis, may eventu- 
ally lead to the appearance of a mutant able to maintain 
itself on the latter. Considering the issues at stake, it is 
worth while expending a considerable sum on this matter to 
test it thoroughly. Meanwhile drastic action is necessary 
to prevent more land being rendered useless and a nuisance. 
Lightly infested areas, with easily eradicable pear, on 
Crown and private lands, must at once be eradicated before 
the plants have gained a stronger hold. It is folly to delay 
action longer, and essential that the present limits of ‘‘in- 
eradicable’’ pear should not be extended by further neglect. 
Introduced Plant Pests.—In every direction one sees the 
extension of noxious weeds, and new species are frequently 
