If, on the other hand, under the above-mentioned conditions of unrestricted development, without competition, variations were determined by “_mechanical principles_,” then, according to Nägeli’s view, all plant forms that now exist would still have evolved, and would be found living at the present time, but along with all those that now exist there would be still other forms in countless numbers. These would represent those forms which have been suppressed. On Nägeli’s view competition and suppression do not produce new forms, but only weed out the intermediate forms. He says without competition the plant kingdom would be like the Milky Way; in consequence of competition the plant kingdom is like the firmament studded with bright stars. The plant kingdom may also be compared to a branched tree, the ends of whose branches represent living species. This tree has an inordinate power of growth, and if left to itself it would produce an impenetrable tangle of interwoven branches. The gardener prevents this crowding by cutting away some of the parts, and thus gives to the tree distinct branches and twigs. The tree would be the same without the watchful trimming of the gardener, but without definite form. Nägeli states: “From my earlier researches I believe that the external influences are small in comparison to the internal ones. I shall speak here only of the influences of climate and of food, which are generally described as the causes of change, without however any one’s having really determined whether or not a definite result can be brought about by these factors. Later I shall speak of a special class of external influences which, according to my view, bring forth beyond a doubt adaptive changes.”