CH. II] THE PODOSTEMACEAE 15 



have gone on. What natural selection undoubtedly does is to 

 work with the individual, and to kill out, upon the whole, those 

 individuals that are below the average in any species— man or 

 animal or plant — but we have no proof that it works in the same 

 way with species as a whole or as units, killing out one species or 

 variety to make room for another, unless in particular conditions 

 which are more or less local. A species a may be killed out in one 

 place, because of unsuitable local conditions, whilst its rival h 

 may be killed out in another, for the same reason. If structural 

 differences go for anything, there must be a great adaptational 

 difference between the Dicotyledons and the Monocotyledons, 

 yet both grow intermingled almost everywhere, and in much the 

 same proportions. There is no " monocotyledonous " mode of life 

 that suits a Monocotyledon better than a Dicotyledon, yet there 

 are very great structural differences between them. 



During this period, the possibility of internal, functional, or 

 physiological adaptation was ignored. Yet adaptation has far 

 more to do with the physiological than with the morphological 

 characters, if indeed it has anything to do with the great bulk of 

 these. There are very few external characters to which one can 

 point as definitely physiological. The leaves, roots, stems, 

 flowers, and fruit are so to a great extent, but not differences in 

 these (such as palmate or pinnate leaves, or drupes and berries), 

 except rarely. Adaptation to climate, which is a physiological 

 difference between one form and another, is primarily a purely 

 internal adaptation. To have any chance of survival, a species 

 must be suited to a greater range of climate than that with which 

 it perhaps began. As it migrates into new territory, it will 

 probably begin to become adapted to the slight changes with 

 which it may meet as it moves with (usually) very great slowness 

 into slightly differing conditions. 



A vast amount of energy was put into the study of adaptation 

 during the last quarter of last century, and the imagination was 

 pushed to the extreme limit to find some kind of adaptational 

 value in even the least important features of plants, such as a 

 few hairs in the mouth of a corolla, an unpleasant smell (to some 

 human beings), and innumerable other characters (cf. books of 

 this period, such as 23). Unfortunately for the adaptationist and 

 for the theory of natural selection, which was founded upon 

 adaptation, no one was ever able to show that the important 

 morphological features of plants, which showed so conspicuously 

 in the characters that marked families, tribes, genera, and most 



