PLANT MORPHOLOGY 63 



in view the limitations which hedge it round: it is to be remembered 

 that the effect of external conditions upon form is always subject 

 to hereditary control, and that thus the whole field of past history 

 is still left open to speculation. This seems to have been forgotten 

 by a recent writer, who remarks that "the future lies with experi- 

 mental morphology, not with speculative morphology, which is 

 already more than full-blown." Though this assertion contains an 

 important truth, inasmuch as it accords prominence to experiment, 

 the case is in my opinion overstated. All who follow the development 

 of morphological science will value the results already obtained 

 from the application of experiment to the problems of plant-form. 

 But it is necessary at the same time to recognize that the two phases 

 of study, the experimental and the speculative, are not antithetic 

 to one another, but mutually dependent: the one can never super- 

 sede the other. The full problem of morphology is not merely to see 

 how plants behave to external circumstances now, and this is all 

 that experimental morphology can ever tell us, but to explain, 

 in the light of their behavior now, how in the past they came to be 

 such as we now see them. To this end the experimental morphology 

 of to-day will serve as a guide, and as a check to the speculative 

 branch, limiting its exuberances within the lines of physiological 

 probability: but experiment can never replace speculation, for 

 experiment cannot reconstruct history. It is impossible to rearrange 

 for purposes of experiment all the conditions, such as light, moisture, 

 temperature, and seasonal change, on the exact footing of an earlier 

 evolutionary period: and even if this were done, are we sure that 

 the subjects of experiment themselves are really the same? There 

 remain the factors of hereditary character, and of competition, 

 which cannot possibly be put back to the exact position in which they 

 once were. There must always remain a margin of uncertainty 

 whether a reaction observed under experiment to-day would be the 

 exact reaction of a past age. So far, then, from experiment competing 

 with or superseding speculation in morphology, it can only act as a 

 potent stimulus to fresh speculation, wherever the attempt is made 

 to elucidate the problem of descent. It will only be those who 

 minimize the conservative influence of heredity, or, it may be, 

 relegate questions of descent to the background of their minds, 

 who will be satisfied by the exercise of an experimental method of 

 morphological inquiry, apart from speculation. 



It has already been remarked that, notwithstanding the sound- 

 ness of Hofmeister's comparison for the alternating generations as a 

 whole, the homologies of the parts remained unsatisfactory: the chief 

 reason for this was that the grouping was not derived from com- 

 parison of nearly allied species; nor does it seem to have been held as 

 important to consider critically whether such parts as were grouped 



