Showing papers in "Taxon in 1972"

Systematic anatomy of the leaf epidermis in the magnoliaceae and some related families

Abstract: Summary Stomatal and other epidermal features suggest a close relationship among the Magnoliaceae, Eupomatiaceae, Degeneriaceae, and Himantandraceae, a somewhat more distant relationship of the Winteraceae to these families, and only a much more distant relationship of the Illiciaceae and Trochodendraceae to this group. Epidermal characteristics of the various genera and species of the Magnoliaceae are highly compatible with the taxonomic scheme of Dandy, and in some respects give strong support to it. The generic separation of Manglietia from Magnolia is particularly supported by my studies. Within the Winteraceae, epidermal features of several species of Belliolum correlate well with the system of A. C. Smith for this genus. The species Bubbia perrieri is anomalous in Bubbia on epidermal features, though clearly a member of the Winteraceae; its taxonomic position merits reconsideration. Many members of the Magnoliales have thickened lamellae (distinct from the outer stomatal ledge) on the outer walls of the guard cells, similar (except in not being lignified) to such lamellae in the modern Cycadales. The presence of these lamellae is considered to be a primitive feature among the angiosperms. Thick-walled epidermal cells with pores in the outer wall are found in many of the Magnoliales, and this feature is also considered to be primitive within the angiosperms. It is noteworthy that the Cycadales also have thick-walled cells, and that in Cycas and some other genera these cells have pores in the outer walls. The vast majority of the Magnoliales have paracytic stomates, and this is considered to be the primitive type within the angiosperms.

Intergeneric hybridization in flowering plants

Abstract: Summary The importance of hybridization in speciation is emphasized by listing most of the known intergeneric hybrids in flowering plants and including a figure (23,675) of all the known hybrids including interspecife ones. No claims are made that the list is complete or absolutely accurate. Some of the strong points regarding hybridization as a process are given. In addition, it is pointed out that hybrids, throughout the range, show both dominance and intermediacy, some possess normal meiosis and many are highly or partially fertile. Although mutation has been given the major role in effecting diversity in the natural world during the first half of this century, it is now quite clear to many biologists, that the role of hybridization in speciation has been

Characters and clustering in taxonomy: a synthesis of two taximetric procedures1

Abstract: Summary The problem of producing a classification from data gathered on specimens has two main components: first the information about the specimens must be structured as characters and character states in such a way that it carries the most information about the taxonomic structure of the objects under study, the mathematical 'noise' being eliminated as much as possible. Then this information must be handled in such a way that a hierarchical partitioning of the objects, called classification, is derived. This paper presents computer-aided methods for the accomplishment of these steps. These methods were worked out to be both mathematically and biologically sound. The character analysis method (called CHARANAL) uses information theory to measure the amount of information common to pairs of characters, and derives from it various measures for the comparison of characters. The clustering technique presented here (entitled GRAPH), on the other hand, is based upon graph theory, and is intended to represent the thought process of the 'classical' taxonomist. For each method are given a general explanation, a detailed explanation of the mathematics involved, an example, and a section on interpretation of results. Resume'

Patterns of species diversity and their explanation

Abstract: Summary Patterns of species diversity and equitability, and the hypotheses suggested to explain them are examined in the terrestrial and marine environments, and the fossil record. Although all the hypotheses are important in explaining diversity, none of them singularly or in various combinations are sufficient to explain the observed patterns. Quantification of the variables suggested to explain the observations will no doubt help clarify and give more credibility to the explanation of diversity, but such studies are only in their infancy. Even the most casual observer notices that all parts of the globe do not contain the same number of species. The great increase in the number of species with decrease in latitude is particularly striking and has been the subject of discussion among biologists for many years. Among the most popular hypotheses suggested to explain this and other observed patterns of species diversity are time-stability-competition-predation-productivity-spa- tial heterogeneity and their various subcombinations (see Pianka 1966, for a review). Recently, there has been an increasing trend toward utilizing not only the number of species present but also measures which take into account the relative abundance of species (species dominance or equitability) as an aspect of species diversity. In this way the observer can utilize the information which previously could only be tabled as a listing of relative abundances. Although some studies of diversity arbitrarily group data from various habitats, such as the number of species present in large quadrats, there has been an increasing trend toward studying species diversity within habitats, and comparing trends between these habitats. In the present paper we will utilize data from both approaches. The purpose of the present study is to review recent and fossil patterns of species diversity and to attempt to make some assessment of our progress in explaining the observed patterns. It is by no means intended to be complete review of all papers dealing with species diversity, as that would require a book of some length and a knowledge of the literature probably beyond the capacity of a single individual. Rather, it is an attempt to summarize the patterns and the adequacy of the hypotheses suggested to explain them from a number of selected papers.

Evolution in the Aegean

Abstract: Evolution in the Aegean , Evolution in the Aegean , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی