528 ALTERATION IN FLORA SINCE 



the indirect influence of man is eliminated, the native vegetation can 

 always hold its own against the introduced. Those plants which have 

 thriven abnormally in this new country, and have impressed visitors 

 by their abundance, are found in settled and cultivated districts, and 

 belong chiefly to what are known as weeds of cultivation, that is^ 

 plants which have become adapted to conditions caused by the direct 

 and indirect action of human beings, and which only thrive where 

 those conditions are maintained. 



In a paper on plant acclimatisation in New Zealand which was 

 published in 1900 I said: 



Seeds of such plants as violets, primroses, cowslips, bluebells, heaths, 

 etc., and of fruits like the bilberry (or blaeberry) and cranberry, have 

 been sown by numbers of persons during the past 50 or 60 years in all 

 sorts of situations, but they have not established themselves. They cannot 

 always succeed even when growing in open competition against the 

 indigenous vegetation, and they never make the slightest headway against 

 many of the vigorous introduced forms. Even where individual plants 

 become established, they nearly always fail to produce seed, and this is 

 the chief reason why such species do not become naturalised. In their 

 native countries their flowers are visited and fertilised by certain species 

 of insects, and these are totally wanting here. Our indigenous insects 

 are unable to fertilise them, and so they do not produce seed. There are 

 no doubt other differences which affect their success in the struggle for 

 existence. The rapidity of germination of their seeds, the subsequent 

 rapidity of growth of the young plants, and many other factors, which 

 have not been sufficiently looked into in this connection, all bear on this 

 question. I have in past years sown quantities of the seeds of many 

 flowering plants of Great Britain along the wayside in one of the suburban 

 roads leading through our Town Belt, but from none of them have plants 

 appeared except from those of foxgloves, whose strong coarse foliage 

 enables it to hold its own against most of its neighbours. If the others 

 have germinated they have nearly always been smothered by cocksfoot 

 or other coarse grass. In gardens many of our European flowers seed 

 now on account of the general prevalence of humble-bees, but many others 

 remain unfertilised. 



Most of the common naturalised plants are capable of self-fertilisation 

 if they are not habitually self- fertilised. For instance the following are 

 found producing seeds in midwinter from flowers which never open and 

 which are more or less imperfect in structure : Shepherd's Purse (Capsella 

 Bursa-pastoris), winter-cress (Barbarea vulgaris), bitter-cress {Cardamine 

 hirsutd), hedge-mustard {Sisymbrium officinale), wart-cress {Senebiera 

 didyma), chickweed (Stellaria media), mouse-ear chickweed (Cerastium 

 glomeratum and C. triviale), groundsel (Senecio vulgaris), sowthistle 

 (Sonchus oleraceus), spurge {Euphorbia Peplus), and perhaps others. This 

 faculty of producing more or less imperfect self-fertilised flowers is almost 

 an essential feature in all such plants, many of which are thus enabled 

 to produce fruit at all seasons of the year, and almost independent of 

 the weather. Another point is that most of them produce very small and 



