136 NEW ZEALAND PLANTS. 



fully, and get the best advice available, before turning any animal 

 loose. Doubtless the same reasoning applies to plants; but, unfortu- 

 nately, they do not wait to be set free. Probably all the worst weeds 

 of the earth have already arrived, and we cannot expect newcomers 

 that would rival the couch-grass (Agropyron repens), the sorrel (Rumex 

 Acetosella), or the so-called " California!! thistle"* (Cnicus arvensix). 

 At the same time, any farmer who sees a new plant on his farm should 

 look at it askance, obtain what information he can get respecting it. 

 and eradicate it at once if he has any reason to suspect it of having 

 the weed-assuming characteristics. 



Finally, there comes in the question whether any of the native 

 plants are liable to extinction. Personally, I should answer this in 

 the negative. There is nearly always some haven of refuge, and, 



O *^ ** 



though many species will eventually become much -more rare, it is 

 most unlikely that anv will be entirely eradicated. 



* This plant is a native of the British Islands, Europe generally, north Africa. 

 and northern to western Asia. It is only naturalised in the United States, where, 

 however, it is called the " Canada thistle." In England it is known as the " corn- 

 thistle " and " creeping thistle," and is a weed of either cultivated or waste 

 ground. 



