November 12, 1914] 



NATURE 



297 



The history of CE. parviflora, L., is no less interest- 

 ing. Morison grew it, and several early specimens 

 are also found in the British Museum. Like CE. 

 biennis, it masqueraded under a pre-Linnaean poly- 

 nomial. Unlike biennis, however, it does not seem to 

 ' ive become naturalised, in Europe, but it was pre- 



; ved in botanic gardens until rediscovered by Miss 

 N. M. Stevens in Maine in 1905, and described in 

 full by MacDougal and Vail. CE. muricata again 

 was named by Linnaeus, but had been introduced a 

 century earlier, as shown by specimens in the Morison 

 Herbarium. 



Qi. angitsiissima has had a somewhat different 

 history. 1 described this species from Ithaca, N.Y., 

 last year, and afterwards found that Morison had 

 cultivated a closely similar race of the same species. 

 The latter probably came from Maryland, where I 

 believe it still exists. Being a weaker species it has 

 not onlv failed to become naturalised in Europe, 

 hut has long since disappeared from the botanic 

 gardens. 



It will thus be seen that the status of CE. 

 lamarckiana differs in no respect from that of other 

 >pecies, and experimental attempts to produce it by 

 crossing two other species are bound to be futile. On 

 the other hand, its open-pollinated habit allows of 

 I ontinual intercrossing of closely related races. But 

 these races naturally occupied the same geographical 

 area, and it is therefore useless to attempt, as has 

 been done, to produce lamarckiana by crosses between 

 two races or species which are geographically isolated 

 from each other. 



Another feature of CE. lamarckiana which it shares 

 with such species as CE. muricata and CE. angus- 

 tissima, consists in the existence of several distinct 

 races differing from each other in minor particulars. 

 The Swedish race cultivated b\- Hcribprt-Nilsson 

 differs from that of de Vries in a number of points, and 

 resembles more closely the CEnotheras cultivated in 

 English gardens. The latter also exhibit various 

 racial differences in addition to the mutations. CE. 

 lamarckiana does not, therefore, consist of a single 

 ' Icmentary species; and in this respect it resembles 

 I lie majority of ordinary wild species. How these 

 racial differences have originated is another question, 

 but they are of a different order from the differences 

 between the mutations. They exhibit one kind of 

 diversity, the mutations another. In other words, 

 there are here two kinds of polymorphism, and they 

 should not be confused with each other. 



The discovery that CE. lamarckiana is an endemic 

 North American species not only dispels the hypothesis 

 that it might have originated in cultivation, but con- 

 siderably weakens the Mendelian assumption that the 

 mutants are merely hybrid combinations, and the 

 mutation process a phenomenon of hybridisation. 

 Since Bateson's original suggestion to this effect in 

 K)02 nearly all the Mendelians have taken a turn at 

 explaining the mutations in this way. We have heard 

 of coupling of characters, duplication of gametes, and 

 innumerable other hvpotheses of this kind applied to 

 the peculiarities of CEnothera. But it has long been 

 obvious to critical students of CEnothera that although 

 CE. lamarckiana may be in some limited sense a 

 hybrid, yet the mutation phenomena themselves come 

 in a different category. And it has remained for the 

 Mendelian assumption to be totally disproved by other 

 lines of attack on the problem. 



The analytical breeding experiments show that 

 something other than Mendelism has to be dealt with 

 in CEnothera, while the cytological work furnishes 

 certain definite clues concerning the nature of the 

 germinal changes involved. The evidence from every 

 hand is so overwhelming that it can no longer be 



doubted that tnutation is a phenomenon of variation, 

 and not merely of inheritance, as Mendelians would 

 have us believe. 



It may perhaps be pointed out here that Mendelism 

 is itself a theory merely of heredity, and a partial 

 theory at that, dealing only with complete or dis- 

 continuous inheritance. The manner of origin of 

 these inherited differences is a matter on which Men- 

 delians have speculated much, and we have had com- 

 plete evolutionary philosophies founded on the pre- 

 sence-absence hypothesis and the supposed universal 

 "loss of factors" in the origin of nova. But it is 

 obvious that a theory of inheritance, or even a know- 

 ledge of inheritance, does not necessarily throw an\ 

 light on the origin of the differences the inheritance of 

 which is considered. In point of fact, instances may 

 be cited in which a character, the evolutionary de- 

 velopment of which was very gradual, has been 

 suddenly lost through a germinal change. It is then 

 inherited in a discontinuous way in crosses with the 

 "loss-mutation." The hornless condition in cattle is 

 a case in point. To suppose that because a character 

 is inherited in discontinuous fashion it has necessarily 

 originated in a similar manner may therefore lead to 

 wholly erroneous conclusions. 



Experiment shows it to be equally untrue, con- 

 versely, that when a new feature originates suddenly 

 it must always be inherited in Mendelian or alternative 

 fashion. It may be alternative, or it may give a 

 permanently blended result, depending in part upon 

 the organism with which it is crossed. 



An example of this kind of behaviour has occurred 

 in breeding experiments with CE. mut. rtibricalyx. 

 This form originated as a heterozygous mutation from 

 rubrinen'is, its offspring splitting into rubricalyx and 

 rubrinervis in a simple 3 : i ratio, the red pigmenta- 

 ton of rubricalyx being dominant. Extensive crosses 

 have been made between rubricalyx and CE. grandi- 

 flora, Solander. The latter species differs throughout 

 from (E. lamarckiana and its derivatives. The most 

 striking differences are in foliage, buds, pubescence, 

 and physiological reactions, CE. grandiflora developing 

 more rapidly at certain stages, and being adapted to 

 a more southern climate. 



In grandiflora X rubricalyx and its reciprocal, the 

 F, hybrids are intermediate in foliage and other 

 features, but the rubricalyx pigmentation is essentiallv 

 dominant, though the depth of red is paler than in the 

 rubricalyx parent. When the rubricalyx parent wa- 

 heterozygous for the red (R) the F, contained, as anti- 

 cipated, 50 per cent, with red buds (R) and 50 per 

 cent, with green buds (r). In the F, families shaqi 

 segregation usually took place, but a few rare cases 

 were found in which the red pigmentation had not 

 behaved as an unmodified unit-factor, but was inter- 

 mediate, i.e. the sepals were paler red with onlv traces 

 of red on the hypanthium. By selling such individuals 

 it was found that a new and intermediate condition 

 of pigmentation had been obtained, for the F3 off- 

 spring bred true to the condition of their parent. In 

 this way a sharp unit-character which has originated 

 through a mutation may be permanently modified by 

 crossing with another species. 



By back-crossing the ordinary F. offspring again 

 with grandiflora the pigmentation is also further 

 diluted, and new conditions of stability in pigmenta- 

 tion are reached. Many of the details of these experi- 

 ments have already been published, and here attention 

 is merely directed to the fact that the Mendelian 3 : i 

 ratio with sharp alternation between the characters 

 appears to depend upon a condition of balance in the 

 organism. If this condition of balance is disturbed 

 by crossing with another species having a different 

 metabolism then the character in question may be 



NO. 2350, VOL. 94] 



