10 XEW ZEALAND PLANTS. 



such small variations would so accumulate that new forms in har- 

 mony with the new conditions would arise. Such forms have arisen, 

 and constitute, in large measure, the plants which are peculiar to 

 New Zealand, and form nearly three-fourths of the flora so far as 



\j 



ferns and flowering-plants are concerned. This is stating the main 

 facts of evolution in very general terms ; no one really knows how it 

 has come about, though no scientists deny the phenomenon. That is 

 to say, evolution is proved up to the hilt, but its methods are still 

 under discussion. 



Three principal theories are in vogue. The first, of which Darwin 

 and Wallace are the illustrious authors, is know r n as the theory of 

 natural selection. It takes the well-known fact that all organisms 

 vary in all directions, and considers that if certain variations are 

 beneficial they will persist, and by degrees, in the course of an enor- 

 mous number of generations, become so intensified that a new species 

 will result. As for the unbeneficial varieties, they will in course of 

 time perish through the conflict with the more fitted. 



Quite recently the eminent Dutch botanist, Hugo de Tries, has 

 shown, by numerous far -reaching experiments extending over many 

 years, that certain varieties, differing markedly from the parent in 

 some hereditary characteristics, appear all of a sudden, and that a 

 new species comes at once into the world without the lapse of long 

 years. If such a species is adapted to its surroundings it will remain : 

 but, if not, it will go to the wall. This is called the mutation theory. 

 Quite a large amount of evidence in favour of this theory is afforded 

 by New Zealand plants, and a most interesting field of study lies in 

 the collecting and growing varieties of variable species, and ascertain- 

 ing how far such are constant and reproduce themselves ' true ' 

 from seeds. Phormium, Veronica, Epilobium, Celmisia. and Ranun- 

 culus are genera which might with profit be studied experimentally, 

 and which will never be properly understood otherwise. 



A third school believes that the direct action of the conditions to 

 which a plant or animal is exposed evokes changes in accord with 

 such conditions. This is called the New Lamarckian doctrine, or the 

 doctrine of the inheritance of acquired characters. For instance, if a 

 plant grows in a wind-swept locality (fig. 4), according to this view, in 

 the course of time its descendants might have the form of wind-swept 

 plants no matter where they grow. Or if a land plant could be grown 

 successfully in water, it might develop special structures peculiar to 



