NATURE 



[November 9, 191 1 



The results of theoretical reasoning are always stated 



with scrupulous cnre, and their limitations clearly 

 expressed, and no at tempt is made to press conclusions 

 based on idealised premises further than the case 

 will warrant. A striking instance of this is furnished 

 by the way in which, after developing his theory of 

 the evolution of the earth-moon system with justifiable 

 enthusiasm ;iiul evident faith, he takes care frankly 

 to point out that other agencies must probably be 

 sought to account for the origin of the satellites of the 

 exterior planets and of the planets themselves. 



H. L. 



RV.VENT ADYASCES IN THE GENETICS OF 



PLANTS. 

 Einfiihrung in die cxpcrimcnicUc Vererbungslehre 



By Prof. E. Baur. Pp. vi + 293. (Berlin : Gebriider 



Borntraeger, 191 1.) Price 8.50 marks. 

 pROF. ERWIN BAUR is well known to students 

 *- of genetics as a most successful investigator. 

 The fifteen lecluic-^ iiulucit'd in the present volume 

 were delivered as a course in Berlin, and they con- 

 stitute an admirable text-book of the subject, which 

 will do much to familiarise Continental biologists 

 with the methods of Mendelian analysis and the deduc- 

 tions to which it has led. The coloured pictures are 

 exceptionally good. No clearer or better illustrated 

 account of the present state of knowledge of these 

 matters could be desired. 



Some years ago Prof. Baur began a series of re- 

 searches into the nature of variegation in plants, with- 

 out any special intention of investigating Mendelian 

 phenomena, but, like so many others engaged on 

 special problems, he soon found that a knowledge of 

 heredity was indispensable to a proper understanding 

 of his subject. The breeding experiments then insti- 

 tuted, though begun as a side-issue, have illuminated 

 the whole field. His first success was obtained in a 

 study of the golden-leaved Antirrhinum, which he 

 proved to be a heterozygous form, possessing only one 

 factor for greenness. Self-fertilised, it gives two 

 yellows to one green, the missing term in the series 

 Ixini,- the homozygous albinos which perish on ger- 

 mination. 



This led to a comprehensive examination of the 

 inheritance of flower-colour in A. majus, a subject also 

 studied by Miss Wheldale in this country. The series 

 of types is very large, seemiiig ai first sight almost 

 contmuous, and the analysis was exceptionally trouble- 

 some, but it is satisfactory to know that though work- 

 ing independently, both observers have arrived at 

 practically the same conclusions as to the factorial 

 composition of the several forms. In this book 

 Antirrhinum is naturally taken as the typical example 

 of the effects of combinations of long series of factors, 

 and the reader who masters this example will have 

 f^ncountered most of the complications which ordinary 

 Mendelian inheritance presents. 



From this work on the varieties of a single species 

 Baur has gone on to less familiar ground, and in this 

 book he gives the first results of his experiments on 

 the mterrelation of forms which are quite distinct 

 species in the systematic sense, especiallv .4. majus 

 NO. 2193, VOL. 88] 



and A. molle. The F, plants are fully fertile, and F,| 

 shows a long series of diverse types resulting from 

 the recombination of segregating factors, but the 

 analysis is still to be completed. One observation of 

 extraordinary interest is announced, namely, that the 

 self-sterility of A. molle is a recessive. This an- 

 nouncement must be regarded as preliminary, but if 

 established, the discovery will constitute a striking 

 advance. Self-sterility is one of the greatest paradoxes 

 in nature. If it is true, as we are almost forced to 

 believe, that a self-sterile plant can be fertilised by 

 the pollen of any other individual but not by its own, 

 then each individual is differentiated by virtue of its 

 individuality, and there are as many classes as indi- 

 viduals. The notion once suggested by de Vries, 

 which I also had formerly entertained, that there are 

 in reality several classes of individuals and that prob- 

 ably fertilisation was inoperative only within <■ 

 class, is negatived by such experiments as have 1 

 made by others and by myself (on a small scale in 

 IJnaria vulgaris). If self-fertility be a dominant, the 

 main mystery is still unsolved, but we have a new fact 

 of great consequence which may lead to a solution. 



The most important chapters are those in which 

 Baur describes his discoveries regarding the inherit- 

 ance of the several forms of " Chimaera," the term 

 Winkler has introduced to denote patchwork or mosaic 

 individuals. In a variegated Pelargonium, for in- 

 stance, the albino parts of the vegetative organs may 

 be sectorial forming radiating patches of white, or 

 periclinal, in which case the external layers of cells 

 may be green and the internal white ; or conversely 

 the internal may be green and the external cells white. 

 Baur has shown that the colour of the offspring, 

 whether green or white, depends on the nature of the 

 subepidermal layer of cells from which the parental 

 germ-cells were derived. If in the periclinal chimaera 

 the two peripheral layers of cells are green, the off- 

 spring (of self-fertilisation) are all green ; if the peri- 

 pheral layers are albino the offspring are all albino, 

 and, of course, perish. If only the outer cell-layer 

 is white the offspring are green. In either case the 

 particoloured character does not reappear in the off- 

 spring. From the sectorial chimaeras the inheritance 

 is more complex, and much remains to be cleared up. 

 This discovery of the significance of the subepidermal 

 layer is one of very great importance, and we may 

 anticipate that it will lead to remarkable extensions. 

 It may not improbably lead to a reconsideratioi. 

 the generally accepted doctrine that segregation t, 

 place in gametogenesis. 



Baur has applied these observations to the inter- 

 pretation of the curious " graft-hybrids " between 

 Solanum nigrum and the tomato, first made by Wink- 

 ler. Some of these were obviously sectorial patch- 

 works of the two species, but Baur suggested that of 

 the others some were actual periclinal chimaeras, in 

 which a foundation of tomato was enclosed in one 

 or in two cell-layers of S. nigrum, or conversely S. 

 nigrum tiuiosed in an outer sheath of tomato tissue. 

 This conclusion was at first strongly resisted by 

 Winkler, but in a preliminary communication he has 

 since announced the proof that it is correct, having 

 himself by cytological investigation of the growing 



