2S4 



THE E VOL UTION OF SEX. 



Or if we take in particular the origin of the flower, which all 

 botanists agree in regarding as a shortened branch, the natural selec- 

 tionist explanation (did the theory trouble itself with such questions) 

 would seem to be, that the flower had arisen by selection from the 

 two other alternatives of lengthened and unshortened axes. But this 

 is at once excluded by the physiological explanation that shortening 

 of the axes was inevitable, since the expense of the reproductive 

 functions necessarily checks the vegetative ones, for it is evident that 

 we can not speak of selection where the imaginable alternatives are 

 physically impossible. So, too, the shortening of the inflorescence 

 from raceme to spike or flowerhead, or still further into the hollowed 

 form of a fig, with the corresponding reduction in the size of the 

 flowers, is again the result of the check imposed by reproduction on 

 the growth of axis and appendages. 



The same simple conception of a continuous checking of vegeta- 

 tion by reproduction, unlocks innumerable problems of floral structure, 

 large and small alike, from the inevitable development of gymnosperm 

 into angiosperm by the continuous subordination of the reproductive 

 carpellary leaf, to the variations of cabbages as seen in the transitions 

 between leafy kale and cauliflower. Or again, the origin of floral 

 color, as primarily an inevitable consequence of the same principle of 

 vegetative subordination through reproductive sacrifices, was long ago 

 pointed out by Spencer, and admits of detailed elaboration without 

 attaching more than secondary importance to selection by insects. 



In another way the antithesis between reproduction and nutrition 

 may be illustrated among the existing orders and species of flowering 

 plants. Just as the lilies, for instance, range on the one side toward 

 the characteristically vegetative grass, or on the other toward the 

 reproductive orchid, so it is with the main variations of every natural 

 alliance. Thus, the Ranunculacccz have their grassy and their orchid- 

 like types in meadow-rue and larkspur respectively, while the species 

 of these very genera show, within narrow limits, similar swings of 

 variation. What we call higher or lower species are thus the leaders 

 or the laggards along one or other of these two lines of variation. 



Among animals, the importance of the reproductive factor may 

 be illustrated in the most diverse series. Thus the greatest step in 

 organic Nature, that between the single-celled and many-celled 

 animals, bridged as it is by loose colonies some of which are at a 

 very low morphological level, is not due to the selection of the more 

 individuated and highly adapted forms, but to the union of relatively 

 unindividuated cells into an aggregate, in which each becomes dimin- 

 ishingly competitive and increasingly subordinated to the social whole. 

 The colonial or multicellular forms, originating pathologically in all 



