430 DARWINISM 



of natural selection, but must be regarded as naturally trace- 

 able to the vegetative checking of their respective types of 

 leaf organ. Again, a detailed examination of spiny plants 

 practically excludes the hypothesis of mammalian selection 

 altogether, and shows spines to arise as an expression of the 

 diminishing vegetativeness — in fact, the ebbing vitality of a 

 species. 1 



Objections to the Theory. 



The theory here sketched out is enticing, and at first sight 

 seems calculated to throw much light on the history of plant 

 development; but on further consideration, it seems wanting 

 in definiteness, while it is beset with difficulties at every step. 

 Take first the shortening of the raceme into the umbel and the 

 capitulum, said to be caused by arrest of vegetative growth, 

 due to the antagonism of reproduction. If this were the 

 whole explanation of the phenomenon, we should expect the 

 quantity of seed to increase as this vegetative growth dimin- 

 ished, since the seed is the product of the reproductive energy 

 of the plant, and its quantity the best measure of that energy. 

 But is this the case ? The ranunculus has comparatively few 

 seeds, and the flowers are not numerous ; while in the same 

 order the larkspur and the columbine have far more seeds as 

 well as more flowers, but there is no shortening of the raceme 

 or diminution of the foliage, although the flowers are large and 

 complex. So, the extremely shortened and compressed flower- 

 heads of the compositse produce comparatively few seeds 

 — one only to each flower ; while the foxglove, with its long 

 spike of showy flowers, produces an enormous number. 



Again, if the shortening of the central axis in the successive 

 stages of hypogynous, perigynous, and epigynous flowers were an 

 indication of preponderant reproduction and diminished vegeta- 

 tion, we should find everywhere some clear indications of this 

 fact. The plants with hypogynous flowers should, as a rule, 

 have less seed and more vigorous and abundant foliage than 

 those at the other extreme with epigynous flowers. But the 



1 This brief indication of Professor Geddes's views is taken from the 

 article " Variation and Selection " in the Encyclopcedia Britannica, and a paper 

 " On the Nature and Causes of Variation in Plants " in Trans, and Proc. of the 

 Edinburgh Botanical Society, 1886 ; and is, for the most part, expressed in 

 his own words. 



