1897] PLACE OF ISOLATION IN ORGANIC EVOLUTION 243 



uncertain and irregular. There is still another reason for coming 

 to the same conclusion. If it be good for a plant to have its flowers 

 fertilised by pollen from other plants, then the grouping of flowers 

 into a head or spike must be injurious, because it almost insures 

 that the flowers shall be fertilised by pollen from other flowers of 

 the same inflorescence, which Darwin says does little or no good; 

 and yet plants with capitate flowers are numerous and prosperous. 



That cross-fertilisation is useful is proved by the fact that all 

 the higher animals are bisexual ; but that it is not essential is also 

 proved by the existence of large numbers of asexual organisms, and 

 by the fact that the highest plants are hermaphrodite. The first 

 phanerogams were, no doubt, diclinous and anemophilous. As the 

 number of species increased the individuals of each species would 

 diminish, and, consequently, fertilisation by the wind would become 

 more uncertain ; and, probably, it is for this reason that the higher 

 angiosperms became hermaphrodite. But this hermaphroditism was 

 tempered by dichogamy, the origin of which is not connected with 

 insect fertilisation. The visits of insects came later. They com- 

 menced to cultivate, as it were, the flowers for their own use, each 

 species trying to preserve the honey for its exclusive benefit ; for it 

 is evident that all these floral arrangements — including colour, capi- 

 tate flowers, scent, etc. — are very useful to the anthophilous insects, 

 for whom the honey is preserved. But these flowers, elaborated by 

 insects for their own benefit, have secured complete isolation for the 

 plants to which they belong, and the variations have therefore been 

 preserved, whether they were useful or indifferent, or even when they 

 were injurious, as in the reduction of stigmatic surface in the 

 orchids, the abortion of one half of each anther in Salvia, and the 

 asexual condition of the ray-florets in some of the Compositae. All 

 the changes, however, are useful to those insects which alone can 

 fertilise the flowers, and Dr Hermann Miiller thinks that different 

 kinds of insects have evolved different kinds of flowers suited to 

 their tastes. In fact, these flowers have been cultivated by moths 

 and bees, just as ants have domesticated some beetles and aphides. 

 The plants that have escaped from their cultivators have run wild 

 again, like rabbits in Australia and New Zealand. 



Isolation by Elimination — or natural selection in Darwin's sense 

 — must always have a utilitarian cause, because the elimination is for 

 the benefit of the remainder — that is, for the selected. It may be 

 a struggle for food, or it may be a struggle for protection against 

 enemies, or it may be a struggle to secure the persistence of the 

 species ; but in all cases it must be a struggle with death as the 

 penalty for being vanquished, because, without elimination by death, 

 there can be no selection and no isolation. It is only the struggle 



