504 INTERACTION OF ENDEMIC 



on the lookout for all sorts of changes in colour, food, nesting habits, 

 colours of eggs, and so on ; trout grew so rapidly in the streams and 

 lakes into which they were introduced as to belie all previously 

 recorded experience. The same thing occurred among plants. Water- 

 cress — a plant of two to four feet in length in European waters — grew 

 in some streams to a length of from twelve to fourteen feet, and with 

 stems as thick as one's wrist; the common spear-thistle, which is 

 from two to five feet high in Britain, formed in some districts vast 

 impenetrable thickets six to seven feet in height; brambles, briars and 

 other weeds took possession of whole districts, and threatened to 

 choke out all other vegetation. It seemed indeed as if the laws of 

 natural selection and the principle of the survival of the fittest had 

 been temporarily suspended, and nature was running riot. 



It is no wonder that all the younger naturalists in the country 

 were almost inclined to think that perhaps we would here see the 

 rise of new varieties, which would become "fixed," and would soon 

 rank as "species," distinct from those from which they were de- 

 scended. It may be that our ideas as to what constituted varietal and 

 specific distinction were somewhat vague — ^in that respect we were 

 not very diff'erent from the majority of those who used these terms 

 in a somewhat loose manner — but there they were. Some such feeling 

 was still in my mind as late as 1891, when I read a short paper 

 before the Biological Section of the Australasian Association for the 

 Advancement of Science at its Christchurch meeting, "On Some 

 Aspects of Acclimatisation in New Zealand." The following sentences 

 show the trend of my views at the time : 



One of the most interesting points connected with the successful 

 naturalisation of foreign species is the observation of the changes which 

 they undergo in their altered conditions. Nearly all our introduced animals 

 have been brought from lands where the struggle for existence is very 

 keen, and where natural enemies abound. In their new home they have 

 been set free from these old trammels, and the enemies have been left 

 behind. Under such circumstances it is not surprising to find that sports 

 in colour, which in Europe would be strictly eliminated as soon as they 

 appeared, owing to their rendering their possessors too conspicuous to 

 their enemies, are here preserved and tend to be reproduced. 



I then went on to instance what occurs among hares, rabbits, sparrows 

 and other birds, humble-bees, etc., both with regard to change of 

 colour and of habits. My mind was evidently quite prepared to find 

 such changes, though I had to admit that the evidence sought for 

 was not forthcoming to any extent. 



The subject continued to occupy my thoughts from time to time, 

 but I was not able to devote much consecutive attention to it until 

 1915, when it seemed advisable to me to resume the thread of my 



