342 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
involved either in selecting introductions or dealing with those that 
threaten to or have run amuck. G. M. Thomson (26) has vividly 
summarized this course in New Zealand. 
The first important list of introduced plants appeared in J. D. 
Hooker’s Handbook in 1867 (15). The latest is that in Cheeseman’s 
Manual, second edition, 1925 (4), since which time other species have 
arrived and more are constantly being introduced by both official and 
private interests. Several publications have been issued to aid in 
identifying introduced plants, as one by Allan (1). In 1922 G. M. 
Thomson brought together the scattered information on introduced 
animals and plants (26). His object in compiling the book was to 
obtain precise data as a basis for understanding what to expect in the 
conflict between the introduced and the native flora and fauna, and 
for drawing up effective future scientifically based control measures. 
He records over 600 species of plants as truly wild, that is, they re- 
produce by seed and appear to be permanent denizens of New Zealand. 
Most of them are of European origin, a few are from Australia, and 
some from America and Asia. 
Although widespread harm has resulted from bringing in certain 
foreign plants, the economy of the country is founded on imported 
species of plants and animals. The list of introduced plants includes 
injurious, potentially harmful, harmless, and both injurious and useful 
species, depending on circumstances. Reference has already been 
made to several harmful species. A potentially dangerous species is 
the prickly pear cactus (Opuntia sp.) which in Australia has been so 
destructive. It was reported in 1840 at Hokitika on the west coast 
of South Island but has not spread. One wonders what would happen 
if a frost-resistant species were released in Central Otago. Red clover 
(Trifolium pratense) came early, but had to wait for the introduction 
of the humblebees to pollinate its flowers before it could set out to 
cover New Zealand. One accidentally introduced weed, the slender 
thistle (Carduus pycnocephalus), which probably came originally as an 
impurity in farm seeds, now is an emergency winter feed for sheep in 
Central Otago. But if the native feed had not been overgrazed, this 
emergency would not arise. An interesting failure seems to be the 
Chinese paper mulberry (Broussonetia papyrifera) reported by Sir 
Joseph Banks on the first Cook expedition in 1769. It was obviously 
a Maori introduction, for cloth was made from its bark fibers, but it 
is not found in New Zealand now, though it is a common weed in 
most tropical and subtropical and warm-temperature countries. The 
common mullein has an advantage not shared by most weeds and 
cultivated plants in that the introduced rabbits and sheep will not 
eat it. 
Many New Zealand introductions show astonishing vigor, rapid 
growth, and large size. This is especially striking in the Monterey 
