Conclusions.—From the preceding sketch of current plant morphology it is seen to be founded on the theory of evolution, used as a working hypothesis. Observed facts are interpreted from the point of view of phylesis, the argument leading towards the reconstitution of evolutionary history. The difference between the older idealistic and the newer inductive morphology has been well drawn by Sachs. He pointed out "that the former fits new facts into a scheme of old conceptions, the latter deduces new conceptions from new facts" (History of Botany, 189o). But morphologists are still bound by an idealistic evolution theory, for some preconceived type is in their minds. The remedy lies in a refusal to accept any conclusion from comparison as definitive, unless based upon consecutive data derived from actual organisms phyletically related one to another. The consequence of this would be a greatly increased recognition of polyphyletic sequences. But it is better to entertain a wide theory of polyphylesis, with that apparent Indefiniteness of conclusion that follows in its train, than to accept questionable doctrines that bring satisfaction only to uncritical minds.
Finally there remains the question of causality. The causes of development can best be unravelled and their relations to the environment established by experiment. On the other hand, experi ment by itself cannot reconstruct history : for it is impossible to rearrange for purposes of experiment all the conditions exactly as they were in an earlier evolutionary period : and even if this were done, can it be assumed that the subjects of experiment will really be the same? Consequently there must always be a margin of uncertainty whether a reaction observed under experi ment to-day would be the exact reaction of a past age. Neverthe
less there is a great future before experimental morphology : and though it cannot wholly unravel the history of form, this should still be approached experimentally as well as objectively.
Thus the way had already been prepared for Modern views, associated with "hormones," and their influence on individual development indicates from yet another angle how morphology is becoming ever more closely knit to physiology. It has been said that it deals with the stereotyped results of physiology. This is true in so far as it points towards the historical aspect of mor phology, extending back as it does to the remotest fossil records: while physiology deals observationally with the reactions of the present time. But a better summing up of the relations of these two branches of biological science would be that morphology deals with all phenomena of form, including such as are not yet physi ologically understood.