How Plants change their Forms.

It has been shown above how a constant warfare goes on between the plant inhabitants of the most quiescent forest or meadow, and how some survive and others perish. This truth forms the corner stone of the doctrine of evolution. Just as there is no actual stability in the vegetation of a region, so is there none in the individual species. Constant change is the undeviating plan of nature.

The original plant-immigrants settling down in their new home would be exposed to novel conditions of soil and climate, and to con tact with other plants and animals. This new environment would possibly bring about slight changes in the organisms, and in time page 10such small variations would so accumulate that new forms in harmony 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 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 known 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 enormous 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 Vries, 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 longyears. 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 ascertaining how far such are constant and reproduce themselves "true" from seeds. Phormium, Veronica, Epilobium, Celmisia, and Ranunculus 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 page 11

Fig. 4.—Effect of Wind on Plant From. In front, Manuka (Leptospermum scoparium); behind, Senecio rotundifolius. Paterson Inlet, Stewart Island.
Lands Department] [Photo, L. Cockayne.

page 12aquatic plants, and these would in time become hereditary. This latter theory is mentioned because a number of New Zealand species appear to afford some confirmatory evidence.