1897] ORIGIN OF SPECIES AMONG PLANTS 175 



obstruction to self-fertilisation produced by the rostellum is 

 common in orchids, and generally occurs in all the species of 

 any particular genus. Yet it is obliterated in PKajus blumei, 

 Chysis aurea, species of Chrysoglossum, Avundinia speciosa, and Evict 

 flavcscens, &c, so that these species set plenty of good seed by self- 

 fertilisation, whereas 40,000 blossoms of Dcndvobiwm spcciosum set 

 one pod. I have already had occasion to allude to the rudimentary 

 organs of Mercurialis, Erodium, &c., which are retained in all the 

 species alike. 



Is Dr Wallace, therefore, justified in making the above asser- 

 tion at all, or in demanding that either useful or useless characters 

 should be limited ? Why should either one or the other be 

 obliterated when a new variation arises ? The fact that a genus, 

 which is the result of sufficient variation in a species (unless it be 

 monotypic), does retain both useful and useless characters in some, 

 many, or all of its species, shows that there are no grounds for his 

 statement. Natural selection may demand it, but nature utterly 

 refuses to be obedient to that theory. 



Too great stress is laid upon a necessary fixity, as a proof of 

 specific characters, by many writers. This is purely a relative 

 matter. Cultivation has been suggested as a test of a species ; but 

 this is the very best means of inducing a wild plant to vary, as all 

 cultivators know. The fixation of any variation is a matter of 

 time. About five years may, perhaps, be regarded as the average 

 period under cultivation in " fixing " races : but nothing is known 

 about wild varieties. In either case the rule is that the environ- 

 ment must be constant. 



Indefinite Variations, non-existent. — This is the second 

 hypothetical source of new variations according to Darwinians. 



With regard to all the offspring varying approximately alike 

 and not " indiscriminately " (Eomanes) or " indefinitely " (Darwin) 

 when subjected to changed conditions of life, I wish to emphasise 

 the fact most strongly that experiments show conclusively that 

 if seedlings are subjected to a markedly different environment, 

 when they grow up to maturity, the rule is, that all that do 

 change, change in precisely the same way. They do not vary 

 indefinitely among themselves ; so that there is no material here — 

 any more than with " individual differences " — for natural selection 

 to act upon. Thus, in cultivating the wild parsnip or carrot, all 

 the seedlings that change, do so by beginning to assume the same 

 new characters — viz., an increased size with a greater fleshiness in 

 the root, larger dimensions of the leaves, reduction of hair, &c, 

 with a corresponding alteration in the anatomical structures. 



So, too, if the seeds of an amphibious plant as Bamtnculus 

 heterophyllus be sown in a garden border, all grow absolutely alike 



