Showing papers in "Taxon in 1967"

An information theory model for character analysis

Abstract: Describing is an essential function of science. Developing more efficient and accurate means of describing has been a primary concern of many investigators, and many diverse means of describing have been used, from mathematical formulae to Latin species descriptions. The problem of describing is of especial interest to workers in areas of research, such as taxonomy and ecology, where large collections of objects (specimens, plant communities, etc.)are to be organized into information preserving structures (such as classifications). Here the problems consist in part of: 1. discovering which properties should be described, and 2. deciding how the descriptions of the properties should be made. Rogers (1963) indicates that this problem is of classical origin and has played a major role in traditional taxonomic studies, but since the techniques for its solution have been largely informal, they have not been subjected to mathematical analysis. Part one of the problem still lies, for the most part, within the professional providence of the worker. The second part has been addressed in many ways. In some cases different descriptive schemes have been empirically tried in an attempt to discover a more pleasing result (Beers et al., 1962). In particular, Rohlf (1965), has described a statistical test to compare two different schemes of describing, when the descriptors are numerical. Analytical techniques from linear algebra (Rohlf and Sokal, 1962) have been used with some success to discover more efficient descriptors. Techniques using statistical methods of correlation are common. In other cases the force of precedent and convention is strong and some traditional scheme is adopted without question. Although much productive work toward measuring the efficiency and accuracy of descriptors has been done, the problem is still real, especially in cases where the descriptors are non-numerical. The following discussion is concerned with a general class of descriptors which are not necessarily numerical. A method is presented for: 1. measuring the interdependence of: a. two descriptors b. two sets of descriptors 2. measuring how successfully a given classification preserves the information in: a. a descriptor b. a set of descriptors. An example of the procedure using a group of orchids is provided.

The taxonomic significance of autopolyploidy

Abstract: Diploid and polyploid populations that are morphologically identical or very similar to one another pose a problem to taxonomists. In the absence of chromosome information, the close morphological similarity would be interpreted as an indication of genetic continuity characteristic of conspecific populations. As soon as a difference in ploidy is known to exist, however, a problem arises because it is well known that barriers to gene exchange of a magnitude characteristic of distinct species are generally found between diploid and polyploid populations. In practice, however, most taxonomists do not give species status or other formal taxonomic recognition to populations differing in chromosome number unless they are able to identify them on the basis of external morphology. On the other hand, taxonomists often apologize for not describing them because of the prevalent notion that such populations are "reproductively isolated" and hence are biological species, whether or not one can distinguish them morphologically. Because of the evolutionary significance of reproductive isolation, many investigators, including myself, have spent a great deal of time looking diligently for minute differences such as pollen size by which chromosome races can be consistently identified and thus formally described in good conscience. Species status has been achieved, we believe, with the difference in chromosome number; we need only find a way to recognize it. Sometimes when we have been unable to find consistent differences in morphology, we have used geographical distribution alone to distinguish between species (e.g., Gayophytum eriospermum and G. diffusum diffusum (Lewis and Szweykowski, 1963). One can reasonably argue, of course, that a difference in distribution is a good character because it reflects a genetic difference which is expressed ecologically. Furthermore, diploids and autotetraploids may appear to be ecologically differentiated even when they occur in the same area, because adjacent populations differing in chromosome number often remain discrete, except for an occasional triploid hybrid. This, at least, has been our experience with Delphinium (Epling and Lewis, 1952). It has become increasingly clear to me, however, that diploids and their autopolyploid derivatives are, by genetic criteria, conspecific because the genetic continuity between them is comparable to that between disjunct conspecific diploid populations. If this is true, there is no reason whatever to treat diploid and polyploid populations taxonomically in a manner different from other conspecific populations, and certainly there is no reason to offer excuses for not having done so. Furthermore, there is evidence to indicate that the presence of discrete populations of diploids and tetraploids within the same area or even geographical replacement is not of itself evidence of ecological differentiation. The purpose of this paper, therefore, is to present the rationale and evidence for these conclusions. Autopolyploids for the purpose of this discussion are considered to be individuals that possess more than two sets of structurally homologous chromosomes each of which if present in a diploid would show a comparable degree of genetic recombination. The barriers to gene exchange between diploids and autopolyploids are well known although their effect on genetic continuity has generally been considered only in terms of preventing gene exchange. It is well known that hybrids between diploids and

The New Willis@@@A Dictionary of the Flowering Plants and Ferns

Abstract: Willis's Dictionary is a famous publication in the world of botany and horticulture. It is a comprehensive and indispensable reference to the generic and family names of flowering plants and ferns. The entries attempt to cover all published generic names from 1753 onwards and published family names from 1789, together with a number of supra- and infra-familial taxa where these have not been based on family or generic names. The generic names include many variant spellings and inter-generic hybrids. Brief characters of subfamilies are usually given. The treatment of the families and higher taxa of the Pteridophyta is based on the classification scheme proposed by Pichi-Sermolli. The synopses of the Bentham & Hooker and Engler & Prand systems are retained. This eighth edition is now published in paperback in order to make it available to a wider readership, not only of professional botanists, but also students and serious amateurs.

Problems in the use of electronic data processing in biological collections

Abstract: Problems in the use of electronic data processing (EDP) in biological collections are explored. To accomplish this, the uses of EDP, actual and potential, are first set forth. The uses are divided into three groups, depending on the source from which the relevant information is obtained. The problems themselves are then grouped into nine mutually exclusive categories. Each problem is discussed in detail. The concept of a decision context is introduced. Its use in making the overall decision as to whether or not EDP should be used in a particular situation is explained. A questionnaire on the problems of EDP in biological collections was returned by 22 curators. Their comments are incorporated into the appropriate places of the text.

Cytogenetic factors associated with the evolution of weeds

Abstract: CORRENS, C. 1928 Bestimmung, Vererbung und Verteilung des Geschlechtes bei den hoheren Pflanzen. Hb. Vererb. II: 1-138. DARLINGTON, C. D. 1958 The evolution of genetic systems. New York. JONES, D. F. 1932 Interaction of specific genes determining sex in dioacious maize. Proc. 6th Intern. Congr. Genet. (Ithaca) 2: 104-107. KIHARA, A. and I. HIRAYOSHI 1932 Die Geschlechtchromosomen von Humulus. 8th Congr. Japan. Assoc. Advan. Sci., pp. 363-367. LEWIs, D. 1942 The evolution of sex in flowering plants. Biol. Rev. 17: 46-67. WESTERGAARD, M. 1958 The mechanism of sex determination in dioecious flowering plants Advan. Genet. 9: 217-281.

The biosystematics of achlys

Abstract: The explanation of distributional disjunctions may shed light not only on the disjunct plants themselves, but also on the more general processes of evolution at work in the botanical world. Specific examples of disjunction from the malvaceous genera Gossypium and Cienfuegosia are discussed. Emphasis is placed not only on their geographical characteristics but on features of their life cycles as well. Two distinct types of disjunction may be noted. On the one hand are found bicentric species wherein the disjunct populations show no demonstrable evolutionary divergence. The distance separating such disjunct populations is generally great, implying long distance dispersal. On the other hand, disjunction is found among pairs or groups of vicarious taxa, wherein the vicariads are clearly differentiated at a specific or infra-specific level. The distances separating such populations may be great or small. The disjunction * Research Geneticist, Crops Research Division, Agricultural Research Service, U.S. Depart- ment of Agriculture, Soil & Crop Sciences Department, Texas A & M University, College Station, Texas, U.S.A. he disposition of two of the three taxa as subspec es of Achlys triphylla is based the large disjunct distribution in combinatio with a striking similarity in mor- hological, physio ogical, and karyological characters. In comparison with these two axa, the third (A hlys californica) d ffers strikingly in morphological, physiological, tological and e ological re pects, as shown in this paper.

Data processing in the herbarium and museum

Abstract: In a recent paper Sokal and Sneath (1966) suggest, among other things, ways in which Electronic Data Processing (E.D.P.) may be used to revolutionize museum keeping in the future. In their understandable enthusiasm for advocating the most advanced methods which exist, and some which as yet do not, they seem at times to be making the museum curator the servant of the machinery rather than the other way round. "If for some reason curators [old-fashioned implied?] would still prefer to have the entire written record attached to the specimen this could be produced by various devices." We believe that the first objective of a museum must be the attachment of a written record to the specimen and that the accuracy of the data contained on the record (or label) must be vouched for by the collector himself or by a member of the curatorial staff. A satisfactory EDP system should be a by-product a bonus -of the initial need to label accurately all specimens kept in the museum. The use of a time shared computer terminal might prove excellent in a large museum which could afford its own central processor, like the Smithsonian Institution or the British Museum of Natural History, but it is not likely that these facilities are going to be available in the near or even distant future to small museums, especially those outside North America and a few countries in Western Europe. For the next decade, at least, it seems more practical to attempt to introduce into museums simple data handling machines which can produce card catalogues and can provide answers not only to the questions listed by Sokal and Sneath but to many others besides. The herbarium and the museum contain collections of specimens and the value of these collections for research and teaching purposes depends largely on the quality of the specimens, their state of preservation, the accuracy of their determination, the completeness and accuracy of the accompanying data, and the geographical coverage and natural variability represented. In order to maintain a first-class herbarium, certain practices are usually followed after the specimens have been received and accessioned. Identification and mounting require the preparation of some type of label or record. A label may be affixed to the herbarium sheet or to a specimen or its container. Then follow sorting and insertion in the herbarium cases, drawers or cabinets according to some artificial or classificatory system. Some herbaria file their specimens alphabetically by family and genus, others follow some classic or current system of taxonomic classification. If the system being followed has numbers assigned to the taxa (for example, the numbers for families and genera as given by Dalla Torre & Harms for the Engler System), these numbers can be used in the sorting and filing processes. Some botanists have argued that a herbarium is an index and does not need an inventory. They forget, apparently, that a herbarium is a type of index which suffers appreciably from use and that it is unique and largely irreplaceable. When specimens are required for study or demonstration they can usually be found directly and extracted without consulting a separate index. There are many other occasions, however, when the specimens could be spared all or most of their handling by first consulting an index. The obvious difference between an index and a herbarium is that

Chromosome and protein differentation in the agropyron scabriglume complex

Abstract: The genus Agropyron (Gramineae) is represented in South America by about 12 species, all of which are polyploid. Some of these polyploids seem to have originated through hybridization between tetraploid Agropyron species and diploid Hordeum (Hunziker 1955, 1966, 1967). Hexaploid Agropyron scabriglume, for instance, (2n = 42) seems to have originated through allopolyploidy between tetraploid Agropyron tilcarense (2n =28) and a diploid Hordeum species (2n 14) (Hunziker, 1966, 1967). In recent contributions the author discussed the possible origin of A. scabriglume and the diversity within it on the basis of morphological, cytogenetic, distributional and biochemical data. This taxon was found to consist of a series of geographically isolated populations most of which cannot be distinguished on morphological grounds. It has been already shown that these populations show striking differences in chromosome repatterning and in the quality of their seed proteins (Hunziker, 1966, 1967). In this brief report the author will present additional cytogenetic evidence on the parental populations and on two new hybrids. Furthermore, new information on the seed protein of most populations is presented. The structure of the whole A. scabriglume complex will be discussed on the basis of the new evidence. The cytological observations were made as previously described (Hunziker, 1966, 1967). The electrophoretic experiments were performed following the same procedure as described by Johnson and Hall (1965). Agropyron scabriglume is a perennial, self-compatible species which has a discontinuous area and is found in damp meadows or river banks from Northern to Southern Argentina. The distribution of this species covers a wide range of latitude as well as altitude. It extends from 3,500 meters above sea level at 22? South Lat. to 100 meters altitude near 38? South Lat. (Fig. 1). It has been found in the valleys of Humahuaca (Jujuy), Cachi (Salta), Tafi (Tucuman), the Precordillera and the Nevado of San Rafael in Mendoza, the mountains of San Luis, the Sierras of Balcarce, the General Acha Valley (La Pampa), the Andes of Neuquen and the Rio Negro Valley. It has not been found in the extensive plains that separate some of these mountain regions (Hunziker, 1967). In general, there are no morphological differences between these populations. There are only three that can be easily separated from the rest on morphological grounds. One is from San Martin (San Luis Prov.), which has pubescent upper surface of the leaf blade; the other two populations have geminate spikelets in almost or nearly almost all of the spike nodes. The latter have been found recently in El Carancho (La Pampa Prov.) and Balcarce (Buenos Aires Prov.) (Fig. 1). There are, however, ecological differences between most of these races which become evident when they are cultivated in a uniform environment. In the environmental conditions of Castelar, Buenos Aires Province, at sea level, with warm summers, the San Martin strain is the most precocious; the La Quiaca strain has

Biosystematic consequences of ecotypic and chromosomal differentiation

Abstract: are not necessarily better adapted to a particular site than their diploid progenitor; they may occupy a given site merely because they have a much greater chance of establishing a colony from a single individual. Once established, a normally outcrossing sexually reproducing autopolyploid population is immune from direct competition by conspecific diploids because diploid immigrants will either fail to leave progeny by hybridization or will merely contribute to the genetic endowment of the population. Diploids and their autotetraploid derivatives may subsequently become differentiated, but if so it will be comparable to that which occurs between populations having the same chromosome number.

Selection of Lectotype Species for Genera of the Family Araceae

Abstract: In the course of preparing Index Nominum Genericorum texts for the family Araceae it has been necessary to make selections of lectotype species. The family is relatively small, and so it has been possible to make selections rather easily in most cases. The reasons for these choices are given here so that later workers can review the selections and make corrections when necessary. A few cases are particularly difficult and will be withheld until work on all generic nomenclatural problems is finished and can be published a a unit. In the meantime there is no reason to withhold what has been completed. I want to thank particularly Dr. J. J. Swart (Utrecht), Dr. F. R. Fosberg (Washington), Mr. C. V. Morton (Washington), and Mrs. M. F. Southwell (ING) for their thoughtful considerations and criticisms freely given during the preparation of this paper.

Notes on the divisions chlorophyta, chrysophyta, pyrrhophyta and xanthophyta and the family paramastigaceae

Abstract: Pascher, 1932(c), p. 567, described the genus Bicuspidella with two included species: B. incus Pascher, 1932(c), p. 567, text-fig. 1, pl. 7g, h, and B. rostrumaquilae Pascher, 1932(c), p. 567, text-fig. 2, pl. 7i. To date neither of these has been piaked as the type species of the genus Bicuspidella Pascher. Bicuspidella incus Pascher, 1932(c), p. 567 is here designated as the type species of Bicuspidella Pascher, 1932(c).