BOTANY 139 



other suitable methods. In such a fashion very many delicate larvae of echinoderms 

 and crustaceans have been reared. 



Heredity, Variation and Mendelism. 



The most active workers on all subjects connected with inheritance (see E. B. xiii, 

 350 et seq.) continue to be those who were stimulated by the rediscovery of Mendel's 

 theories (see E. B. xviii, 115 et seq.). On the experimental side their observations con- 

 tinue to increase in bulk, interest and importance. Biffen, for instance, has succeeded 

 in producing a useful variety of wheat by crossing valuable wheats, liable to the attacks 

 of rust, with less valuable but immune races, interbreeding the hybrids of the first 

 generation, and selecting from their progeny a stock which combines the valuable 

 qualities of the one set with the immunity of the other set. Other investigators have 

 produced comparable results by other methods, but Biffen's work was prosecuted on the 

 lines suggested by the followers of Mendel, and can be readily interpreted, as indeed 

 Biffen interprets them, in the theoretical language of Mendelism. 



From the point of view of theory, the sharp contrast with other views, which appeared 

 to delight the Mendelian school in the early days of its exuberance, is becoming more 

 and more blurred. It was urged, for instance, that Mendelian inheritance was almost 

 a demonstration of the views of those who held that, because species are discontinuous, 

 they had arisen by discontinuous variation (see E. B. xxvii, 906 et seq.}. It now 

 appears that amongst continuous variations some may be due to " fluctuation," and 

 others may be Mendelian mutations. The argument from size of variation has gone, 

 and with it the attractive suggestion of a causal connection between the discontinuity of 

 species and that of variation. We are back to the theoretical position of Darwin, and 

 have to make a choice, as he did, between the probability of the one set or the other 

 being more important. Further experimental results have broken down the conception 

 of the sharp contrast between "dominant" and "recessive" characters. If allelo- 

 morphs always exist in pairs, one possessing a factor absent in the other, the inheritance 

 of colour does not fit the conception of dominance. It is supposed that the colour- 

 factors stand in series, and that the presence of the higher member of a series obscures or 

 prevents the development of a lower member. Thirdly, the Mendelian proposition 

 that the members of an allelomorphic pair are completely segregated in the gametes, 

 which was originally regarded as the distinctive feature of Mendelism, is breaking down. 

 In some cases there is either incomplete segregation or even complete fusion of what 

 were regarded as alternative characters, and if the conception of purity of the gametes is 

 to be maintained, a new analysis of characters must be made. 



It remains to be said, however, that by far the greater part of the modifications, 

 attenuations and extenuations of the original theory of the Mendelians has come about 

 not from the criticism of those who are hostile to their views, but as their own inter- 

 pretations of the results they have obtained. They have found a new organon and are 

 employing it to the lasting benefit of science. (P. CHALMERS MITCHELL.) 



BOTANY 1 



The past few years have witnessed important changes in the modes of the study of 

 plants. Formerly direct observation was the means chiefly adopted in order to extend 

 the fringe of knowledge, but at the present time, the method of advance by way of 

 experiment has spread to almost every branch of the science, and the habits of thought 

 thus induced are influencing the point of view even in departments from which the 

 method itself is excluded from practice. Plant physiology from its inception has been 

 avowedly experimental, but morphology and taxonomy are also yielding to a force 

 which everywhere tends to render the too rigid ideas of a past time more fluid, and con- 

 sequently more fitted to embrace the facts which a wider knowledge has disclosed. 



Genetics. The new science of genetics utilises plants no less than animals for its 

 material, and is eminently experimental. The remarkable results which it has achieved 



1 See E. B. iv, 229 et seq. (and articles referred to, p. 302). 



