May 12, 1910] 



NATURE 



J05 



<' tTerent countries some two hundred forms, differing 



en in extremely minute characters, but which he and 

 . iier observers found to be stable in cultivation. 

 Most systematists regard them as mere varieties. But 

 species are only the stable forms of diverging races, 

 the connecting links between which have disappeared. 



naturalist will unite in one species in the Linnean 

 nse, as in the case of Draba verna, a range of 

 forms where it is conceivable that the differences 

 could be bridged by continuous variation. Darwin 

 thought that such forms might be stable, as, indeed, 

 they appear to be. They may, in fact, be regarded 

 as adjusted to slight differences in the environment, 

 a view which derives some confirmation from the fact, 

 which I confess surprised me, that de Vries finds only 

 one of the two hundred forms of Draba verna in the 

 neighbourhood of Amsterdam. This view would, of 

 course, be rejected by de Vries, who looks upon them 

 by analogy as mutants. The Darwinian explanation 

 equally rests on an analog}-, the production of the 

 races of cultivated plants by artificial selection. 



De Vries feels the force of this, and it is therefore 

 essential to his case to break down the analogy. He 

 admits (p. x) that "the process of selection has 

 enabled us to produce improved races." But he 

 draws a curious distinction between horticultural and 

 agricultural methods. "In horticulture, varieties arise 

 by mutations. ... In agriculture, the highly improved 

 races arise gradually through selection " (p. 82). For 

 my part I am quite prepared to admit that mutation 

 has had some share in the production of the latter; 

 and as to the former, de Vries quotes my own obser- 

 vations on Cyclamen latifolium, where there can be no 

 doubt that the existing race is the result of con- 

 tinued selection. The distinction, in fact, cannot be 

 sustained. 



De Vries objects to any argument drawn from culti- 

 vated races. We know little usually of their origin 

 (PP- 13. H)> and this is true; they are often of hybrid 

 origin (p. 75), which is equally true; both objections, 

 it may be noticed, have been urged against his own 

 CEnothera; finally, "improved races" (unless arising 

 by mutation) lack stability (p. 120). This has been 

 fully discussed by Darwin, and both he and Sir 

 Joseph Hooker insist "on what little evidence this 

 belief rests" ("Variation," ii., p. 32). Such races are 

 the result of artificial selection, and are only stable 

 under artificial cultural conditions. If these are 

 withdrawn a new adjustment has to be sought, and, 

 as Wallace has pointed out, in the face of competition 

 for which they are in no way fitted. As Darwin says, 

 •" to assert that we could not breed our . . . esculent 

 vegetables, for an unlimited number of generations, 

 would be opposed to all experience" ("Origin," fifth 

 edition, p. 16). The fact is accepted in the law courts, 

 and if a pea such as Veitch's Perfection did not come 

 true from seed, the purchaser would have a cause of 

 action against the vendor. 



De Vries states (p. 124) that " frui^-trees grown 

 from seed quickly revert to the original type." This 

 is too extreme a statement. The measure of truth in 

 it is easily accounted for. Stability can be obtained in 

 races where seminal reproduction can be quicklv re- 

 NO. 21 15, VOL. S^] 



peated. But a generation of fruit trees approximates 

 to that of mankind, and though, theoretically, stability 

 might be obtained, it would require a Methuselah to 

 do it. 



De Vries prefaced the first edition of this book by 

 remarking that "The origin of species has so far 

 been the object of comparative study only." It must 

 always be to his credit that he has been the first to 

 submit it to experiment. If the results seem so far 

 inconclusive, the method, in the long run, must be 

 fruitful. Darwin deliberately relied on continuous 

 variation, de Vries relies on discontinuous. It must 

 be obvious that the former has been a potent solvent 

 of a wide range of biological problems where de 

 Vries leaves us without an answer ; and he frankly 

 admits that on the fundamental principle we are as 

 much in the dark as ever. For mutations, "we can 

 as yet assign no cause " (p. 130), though (p. 207) he 

 suggests that " the opportunity for the appearance of 

 mutations is at once given " by change of environ- 

 ment. Beyond this we are no wiser as regards one 

 kind of variation than as regards the other. We are 

 evidently a long way from that " control of the muta- 

 tive process" which "will, it is hoped, place in our 

 hands the power of originating permanently improved 

 species " (p. x). W. T. Thiselton-Dyer. 



PHYSICAL SCIENCE IN THE TIME OF NERO. 

 Physical Science in the Time of Nero; being a TranS' 



lation of the '' Quaestiones Naturales" of Seneca. 



By J. Clarke, with notes on the treatise by Sir 



Archibald Geikie, K.C.B., P.R.S. Pp. liv + 368. 



(London : Macmillan and Co., Ltd., 1910.) Price 



I05. net. 



THE genius of the Roman people was mainly for 

 action, conquest, and organisation. In the 

 realms of thought they made but few original ad- 

 vances, here showing a striking contrast to the 

 Greeks, whose progress in civilisation some few cen- 

 turies previously had been intellectual rather than 

 material, and made in art, philosophy, and specula- 

 tion as to the deeper problems of life and nature. Of 

 course, western nations owe, and have owed, an 

 immense debt to the intellectual advances made by 

 the Greeks, and there seems little danger that this 

 debt will ever be underestimated. But there is reason 

 to fear that full justice may not be done to the scien- 

 tific progress made by the Romans; and Mr. Clarke's 

 admirable translation of Seneca's "Quaestiones 

 Xaturales " comes verj' opportunely to illustrate its 

 extent. 



As Mr. Clarke points out in his introduction, Lucius 

 .\nnaeus Seneca was an exceptionally able man of 

 many aptitudes — rhetorician, advocate, philosopher, 

 author, politician, and for fifteen years tutor first 

 and latterly also 6me damnee to that monster of 

 iniquity, the Emperor Nero. During his lifetime Seneca 

 must have been best known for his eminence as a 

 politician ; during the many years when he was out of 

 imperial favour, and had no share in politics, he 

 devoted himself to philosophy, science, and author- 

 ship. .\s a philosopher he illustrates the eclecticism 



