March 23, 1922] 



NATURE 



Z^l 



letails of fertilisation is still required ; but, apart from 

 s, we now possess sufficient knowledge of the minute 

 icture and of the development of the wheat plant 

 »r most purposes. . 



The greater portion of Part 2 consists of a series 

 chapters dealing with the classification of the numer- 

 is " forms/" many of which the author has had under 

 jrvation for as many as twenty years. At the 

 itset two wild species, Triiicum aegilopoides , Bal., and 

 dicoccoides , Korn., are recognised, together with 

 jven " races " or cultivated species. Eight of the 

 ter, the small Spelt, Emmer, Macaroni, Polish, Rivet 

 leat, Bread wheat, Club wheat, and large Spelt, are 

 jU-known races ; whilst three, T. orientale, Khorasan 

 leat, T. pyramidale, Egyptian cone wheat, and T. 

 rococciim, Indian dwarf wheat, are new creations. 

 16 first of these consists of a couple of Emmer-like 

 ieties, differing only in awn-colour, which are 

 iracterised by the possession of long glumes and 

 lin. The second consists of a group of five Egyptian 

 leats coming close to the Rivet wheats in most of 

 ;ir characteristics, and in leaf colour, shortness of 

 iw, and ear shape strongly reminiscent of segregates 

 )m crosses between T. turgiduni and T. vtdgare. 

 le third is an equally small group of round -grained 

 )rms coming near T. compactum. The further sub- 

 division of these races into " varieties " follows the 

 well-known system in Kornicke and Werner's " Hand- 

 buch des Getreidesbau." 



But this system is not slavishly adhered to, and 

 here and there noteworthy departures are made from 

 it. For instance, several forms placed by Kornicke 

 in T. durum are rightly transferred to the Emmer 

 group, T. dicoccum. Persian Black, too — a form 

 which has puzzled more than one systematist — is also 

 placed in this group, to the satisfaction of those 

 interested in the genetics of this important mildew- 

 resisting wheat. 



In the smaller groups the sub-division of the varieties 

 into forms is a comparatively simple matter, but 

 difficulties occur in the large races, such as T. vulgare. 

 If, by way of example, one takes the first of the beard- 

 less varieties of the bread wheats, T. v. albidum, one 

 finds detailed descriptions, under either a name or a 

 number, of a dozen forms from various parts of the 

 world, supplemented by excellently reproduced photo- 

 graphs of the more distinct types. But the forms 

 themselves are capable of further sub-division. Under 

 the description of Wilhelmina, for instance, is the state- 

 ment : " Similar to this is Willem I. from Holland, 

 Victor, Stand Up, Essex hybrid. . . ." Some of these 

 ;ire almost unquestionably synonymous, whilst some 

 re distinct wheats, and a classification failing to differ- 

 ' ntiate these will disappoint many who grow wheat. 

 NO. 2734, VOL. 109] 



But, whatever the needs of the wheat-grower for 

 a still finer differentiation of forms, one feels that the 

 day for these elaborate descriptions is passing and that 

 it is unlikely that many attempts will be made in the 

 future to bring together and catalogue the world's 

 numerous wheats. Even now, when the subject of 

 wheat-breeding is in its childhood, the geneticist foresees 

 the possibility of an accession of new forms which would 

 reduce Prof. Percival's collection to the dimensions of 

 a dwarf. Such a feature as the winged glume figure in 

 Plate 179 is known to him only in one form. But it is 

 inherited as a unit character, and though scores of 

 forms with similar glumes are in existence at the Plant- 

 Breeding Institute at Cambridge, many more could 

 easily be raised. Much the same is true of that still 

 rarer feature, the purple colour of the grain, seen in 

 T. d. arraseita, which has in the hands of the hybridist 

 given rise to a series of purple-grained Macaroni and 

 Polish wheats, in addition to other forms of Emmers. 

 To cope with such a " flora," the systematist of the 

 future will probably have recourse to brief formulae 

 expressing the genetic constitution of each form — a 

 system which would have many of the merits of that 

 used in the classification of bacteria. 



The systematic portion of the monograph is followed 

 by a chapter of considerable interest on the origin 

 and relationship of the races of wheat. Evidence from 

 various sources — archaeological, ecological, pathological, 

 genetical, etc. — is skilfully marshalled to show their 

 probable lines of development. The story is too long 

 to discuss within the limits of a review, but Prof. 

 Percival's conclusions on the origin of the bread wheats 

 {T. vulgare) are too interesting to pass over. At 

 present, as is well known, no wild species even sugges- 

 tive of this group has been found. A study of the 

 morphology of the wild and cultivated wheats has led 

 the author to the conclusion that " there is not nor 

 has there ever been a prototype of the bread wheats." 

 And further : " The characters of T. vulgare and its 

 allies appear ... to be those of a vast hybrid race, 

 initiated long ago by the crossing of wheats of the 

 Emmer series with species of ^gilops." It so happens 

 that many crosses have been made between the reputed 

 /Egilops parents, ^. ovata and M. cylindrica, and forms 

 from practically all the races of wheats ; but such 

 crosses yield, at the most, sterile hybrids. The signifi- 

 cance of this fact is recognised, but disposed of by the 

 assumption that natural hybrids between the wild 

 iEgilops and the Emmer prototype are more fertile 

 under their native climatic conditions than in Central 

 or Western Europe. 



A chapter on yield follows a useful summary of 

 most of the more important literature dealing with 

 the hybridisation and improvement of wheat. In this 



