Advances in Genetics. Vol. IV. by M. DemerecReview by: H. L. K. WhitehouseNew Phytologist, Vol. 51, No. 2 (Aug., 1952), pp. 275-277Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2428767 .

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Reviews 275 Native Orchids of North America. By D. S. CORRELL. iol x 63 in. Pp. 399 with I46

plates, and 7 text-figures. Waltham, Mass., U.S.A.: The Chronica Botanica Co.; London: Wm. Dawson and Sons Ltd. I950. $7.50.

This competent monograph of the orchids of North America, north of Mexico, has been written by an author who is acquainted not only with herbarium material but also with the plants in the field. It is the first comprehensive work on the orchids of this area, although a number of regional treatments of orchids has been published. The wide variety of climatic conditions in this vast region allows the existence of species not only of genera characteristic of temperate climes but also of genera such as Epidendrum amd Oncidium which attain profusion in tropical America.

The arrangement of the genera follows the system proposed by Schlechter and the species have been arranged alphabetically within the genera. The author has a fairly wide concept of species but published varieties and forms are given consideration. Putative hybrids are also recognized. The descriptions of species are clear and adequate and follow a similar format throughout; the known geographical distribution of each species is given. Although the localities and collectors of type specimens are included, it would have been useful if the whereabouts of the type specimens. had been mentioned. Synonyms of the recognized species are quoted, but references to their publication have been omitted and the reader is referred to Ames's Enumeration of the Orchids of the United States and Canada.

Short but interesting notes on the range of habitats of the various species are given, and further information may be obtained from the cultural notes contributed by Dr E. T. Wherry and Mr J. V. Watkins. Occasionally short journalistic essays describing the author's reactions on finding species in their natural environment have been included in the text, but it is felt that these are rather out of place and mar the general tone of the monograph. The great majority of the numerous plates in this work are of a very high standard, but a few could have been replaced to advantage by clear line drawings. The keys to the species are explicit and have been found to work well. Flower colour has been used occasionally as a character in these keys, a choice which could lead to difficulties in the identification of poorly labelled herbarium specimens. However, there is little doubt that Dr Correll's monograph contains a wealth of valuable information, and is an excellent contribution to the knowledge of the Orchidaceae. E. A. C. L. E. SCHELPE

Advances in Genetics. Vol. IV. Edited by M. DEMEREC. PP. 343. New York: Academic Press, Inc. $7.50.

The publication of a new volume in the series Advances in Genetics is now an event regularly awaited as providing a valuable series of reviews of the diverse topics which come within the scope of that subject. The latest volume, no. iv, is no exception: it contains nine articles, all of a high standard and covering a wide range of subjects. Two deal with gene action in animal development (the mouse and Drosophila); two with the cytology of important animal groups (the Vertebrates and Orthopteroid Insects); two with the genetics of plants of economic importance (coffee and rice); one with plant-breeding methods (as applicable to the cotton plant); and two with the more academic side of genetics: the function of heterochromatin, and the evolutionary significance of gene duplication.

'Physiological Genetics of the Mouse' by S. Gluecksohn-Waelsch and 'Developmental Action of Lethal Factors in Drosophila' by E. Hadorn, deal with studies of development in the best ' genetic' Vertebrate and the best 'genetic' Insect, respectively. Needless to say, highly evolved organisms such as these have an exceedingly complex developmental history with a large number of genes affecting each organ, and hence are unsuited to precise analysis of gene action. On the other hand, there are more gene-controlled processes which can be studied in these organisms than in simpler forms, and moreover, their study allows a better understanding of development in higher animals generally including man. Thus, developmental studies of mice carrying mutations causing pituitary dwarfism and harelip should add to our understanding of these conditions in man. A finding of great interest in the study of gene action and cell differentiation is the occurrence in chromosome IX of the mouse of many genes controlling embryonic growth. According to Gluecksohn-Waelsch, no mutation with other effects has yet been found in this chromosome.

'The Chromosomes of the Vertebrates' by R. Matthey and 'Cytogenetics of Orthopteroid Insects' by M. J. D. White, survey current knowledge of the chromosome cytology of these large

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276 Reviews groups. Data on chromosome number and morphology are still grossly incomplete, particularly in the Vertebrates, and conclusions are necessarily often tentative. Both authors emphasize the importance of the number of long chromosome arms of 'fundamental number', which frequently shows much greater constancy within a group of related forms than does actual chromosome number. In several instances, particularly in the Vertebrates, there is unwarranted acceptance of the direction of evolutionary change. Thus Matthey (p. I70) discusses the role of centric fusion in the evolution of chromosome numbers in Reptiles, apparently implicitly accepting that change of chromosome number has proceeded by fusion of two chromosomes with subterminal centromeres to give one with a median centromere. No reference is made here to the possibility that the process might have occurred in the opposite direction, though Matthey subsequently implies that the process has in fact proceeded in the reverse direction, when he states (p. I74) that there is a 'relation between a low chromosome number and a primitive systematic position'. Similarly, White (p. 272) attributes variation in chromosome number in crickets in part to centric fusion without presenting the evidence for this conclusion. However, in discussing chromosome numbers in short-horned grasshoppers and locusts (p. 275), he gives reasons for believing that the primitive condition in this group was a set of chromosomes all with subterminal centromeres. Both Matthey and White discuss the occurrence of polyploidy in their respective groups, and White describes in some detail the parthenogenetic long-horned grasshopper, Saga pedo, which is undoubtedly tetraploid. As the most likely instance of polyploidy in Vertebrates, Matthey refers (p. I78) to European dormice where one species, Glis glis (the 'Fat Dormouse' of the European continent and not 'The Dormouse' as Matthey implies), has a chromosome number of 2n = 62, while three other species have numbers ranging from 48 to 52. However, this is less suggestive of polyploidy than the instance of the fox and the wolf where 2n =38 and 78 respectively. The following points in Matthey's review are unsatisfactory: It is not always clear whether haploid or diploid chromosome numbers are being quoted. The terms homozygotic and heterozygotic are frequently used in the sense of homogametic (XX) and heterogametic (XY). Finally, for references the reader is fre- quently referred to another review by the author. White's survey, on the other hand, does not suffer from these defects. It is a most valuable contribution, and in addition to bringing together a vast amount of work on chromosome numbers in the Orthoptera, the author also discusses many cytological peculiarities of outstanding interest found in this group. First, there is the confirmation (p. 290) of the discovery made by Payne in I 9I2 in males of the North American mole cricket of an exception to the Law of Independent Segregation of Chromosomes: an unequal chromosome-pair invariably shows the larger member passing to the same pole as the X-chromosome at first ana- phase of meiosis. Secondly, there is the idea (p. 285) that localization of chiasmata is associated with the distribution of heterochromatin. Thirdly, there is the apparent absence of chiasmata in some mantids (p. 289). Fourthly, there is evidence for the evolution of XY-sex-determining mechanisms secondarily from the XO-type which is basic in Orthoptera. Incidentally the existence of an X1X2 Y-system (p. 292) in certain mantids, is claimed as an 'almost unique' case where monophyletism can be deduced from cytology. However, this claim should perhaps be restricted to the animal kingdom, for many instances are known in plants where chromosome numbers conclusively demonstrate a monophyletic origin, e.g. the subfamily Pomoideae of Rosaceae. Fifthly, there is the extraordinary variability of chromosome morphology within many species of Orthoptera, and it is an interesting idea (p. 308) that a shift in the position of the centro- mere of a chromosome may lead to suppression of crossing-over in 'centromere-shift heterozy- gotes' and hence favour the maintenance of hybrid vigour.

'The Genetics of Coffea' by C. A. Krug and A. Carvalho and 'Genic Analysis and Linkage Relationship of Characters in Rice' by S. Nagao, are surveys of current knowledge of inheritance in these economic plants. In both, the genetic study is still in its infancy, in coffee largely on account of its shrubby character and hence long generation-time, and in rice partly because of lack of co- ordination of research. Nagao proposes a standardized system of nomenclature for mutants in rice, comparable to that adopted in maize and Drosophila, and it is highly desirable that such a system be generally accepted. Anthocyanin coloration in the leaves of rice appears to be controlled by three genes PI (purple leaf blade), Pla (purple leaf apex) and Plm (purple midrib). Since these factors are apparently non-allelomorphic, the use of the term allele in describing them on pp. I88 and I 89 is confusing. It would appear that genetic studies of the African genus Coffea, which have been carried on largely in Brazil, have been handicapped by lack of material of all but a few of the species, owing to import restrictions designed to avoid infecting the American coffee plantations

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Reviews 277 with the rust-fungus Hemileia vastatrix. This is particularly unfortunate since the most important species economically, Coffea arabica, appears to be an allotetraploid, and it would be desirable to find its diploid parents (or their nearest living descendants), with a view to increasing the genetic variability available for selection. This point is emphasized by T. R. Richmond in his review 'Procedures and Methods of Cotton Breeding with Special Reference to American Cultivated Species', when he writes (p. 2I9): 'The importance of genetic variability in the primary breeding material cannot be overemphasized, for it is axiomatic that the breeder cannot bring out through selection anything more than is inherent in the raw breeding material.' One of the most out- standing achievements in cotton-breeding, referred to by Richmond on p. 228, has been the arti- ficial induction of polyploidy by means of colchicine in the hybrid between an Asiatic species and a wild American species of Gossypium, and the finding of unexpectedly strong fibres in individuals from crosses between the artificial tetraploid and American cultivated cotton (natural tetraploids of similar origin).

'Localization and Function of Heterochromatin in Drosophila melanogaster' by A. Hannah, and 'Possible Significance of Duplication in Evolution' by S. G. Stephens, are contributions to pure as distinct from applied genetics. Hannah presents an excellent survey of knowledge of hetero- chromatin in Drosophila, and reveals a need for more precision of nomenclature. Thus, although 'Heitz (I928) introduced the term heterochromatin to describe special regions of the mitotic chromosome which retain a dense and compact structure during interphase' (Hannah, p. 88), yet 'intercalary heterochromatin is not cytologically differentiated from euchromatin' (Hannah, p. I20). Stephens's article is concerned with one of the most fundamental problems in the study of evolu- tion: the origin of unlimited hereditary variation. He points out that if one accepts the idea that each gene controls only one primary process as a consequence of a specific surface structure, then gene mutation at best could only replace a finite number of functions by an equal number of new ones, through changes in surface structure. It is thus possible that duplication of loci plays a vital part in evolution, and Stephens gives an interesting account of the evidence, from diverse sources, supporting this hypothesis. However, no mention is made of the instances in Neurospora of close linkage between loci of similar function, where there are favourable prospects of obtaining valuable evidence.

This book is to be recommended to all who can afford it and who wish to keep abreast of advances in genetics. H. L. K. WHITEHOUSE

Flora of the British Isles. By A. R. CLAPHAM, T. G. TUTIN and E. F. WARBURG.

4x X 2 in. Pp. 159I with 79 text-figs. Cambridge University Press. I952. 50s.

It has for very many years been the experience of British botanists visiting foreign colleagues that sooner or later the inevitable question would arise: 'Why is there no recent Flora of the British Isles to which we can refer?' Now at least we need no longer mumble an excuse, for the task has been accomplished; and soon we may hope that all botanical libraries and institutions everywhere will have their copies of 'Clapham, Tutin and Warburg'.

The new Flora will obviously fill a gap; the authors would, however, be the last people to claim any approach to finality or perfection about their work, and indeed confess in their Preface that they are fully aware that 'it has many deficiencies and will doubtless be found to contain errors'. Two general criticisms of the work may be made with justification: first, that the divided authorship and limitations of time have resulted in inequalities of treatment, a fact which is fully conceded in the Preface, and probably inevitable; and, secondly, that the choice of alien species for inclusion seems to have been made on a very different basis in different groups. Thus rare casual Crucifers such as Enarthrocarpus lyratus (Forsk) DC. are included, whilst the well-naturalized Breckland Solanum trifiorum Nutt. is omitted. One should hasten to add, however, that the inclusion of aliens at all is such a welcome departure from the rigid tradition of Hooker's Students' Flora that minor irregularities of selection are unimportant. The most likely general criticism of the Flora will, one feels, be directed against the many changes of name. Although most of these are necessary to bring our usage into line with that of other botanists in agreement with the International Rules, one must also admit that changed concepts of generic limitations are responsible for a good many; and it is here that many will wish the authors' attitude had been more conservative, even where, as in the cases of Scirpus and Bromus, both of which have suffered considerable 'splitting', an entirely logical case for the change can be made.

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