ORGANIC EVOLUTION MACNAMARA. 377 



similar to the parent plant. Self-fertilized seed from these plants 

 (1909) in 1911 produced plants exactly like those of 1907 — i. e., 

 flowers having nine stamens and a style, but no petals. Self-ferti- 

 lized seed from these plants are now (September, 1911) germinating 

 freely. Some of the plants, however, of 1909, in place of a tall 

 single spike, grew some seven or eight shorter spikes, each flower 

 of which had nine stamens but no petals. 



It seems that a certain number of the Fox-glove seeds sown in 

 the year 1906 contained elements in a condition such as that de- 

 scribed by De Vries as being " impressed by an impulsive muta- 

 bility," for some of the flowers produced by these seeds were sports. 

 Seeds from these sports produced their like in 1909; and, further, 

 these latter plants bore some terminal flowers totally different in 

 character from the parent sport from which they were derived. 

 Seeds from these terminal flowers produced their like in the year 

 1911, so that I have now two different strains of Fox-glove plants 

 derived from the seed sown in 1906, and these strains have resulted 

 from self-fertilized flowers — that is, from flowers carefully protected 

 from insects or other means of cross fertilization. It is, however, 

 doubtful if these varieties would have been maintained in a state 

 of nature. While specific stability under constant conditions appears 

 to be the rule in nature, it is widely different in cultivation. When 

 a plant is brought under cultural conditions it maintains its type 

 for some time unaltered, then gives way and becomes practically 

 plastic. 1 It is certain, therefore, that before we can accept De 

 Vries's hypothesis of the origin of species by mutation we must 

 have further and more conclusive evidence on the subject than that 

 which is now available. On the other hand, Huxley's conclusion 

 regarding the Darwinian hypothesis still holds good. He states 

 that all species have been produced by the development of varieties 

 from common stocks; the conversion of these, first into permanent 

 races, and then into new species, by the process of natural selection, 

 which process is essentially identical with that of artificial selection 

 by which man has originated the races of domestic animals, the 

 struggle for existence taking the place of man; and exerting, in the 

 case of natural selection, that selective action which he perforins in 

 artificial selection. 



The evidence brought forward by Darwin in support of his theory 

 is of three kinds. First, he endeavors to prove that species may be 

 originated by selection; secondly, he attempts to show that natmral 

 causes are competent to exert selection; and, thirdly, he tries to 

 prove that the most remarkable and apparently anomalous phe- 

 nomena exhibited by the distribution, development, and mutual 



i Nature, Nov. 28, 1907. 



