Showing papers in "Botanical Review in 1976"

The host range of crown gall

Abstract: Crown gall is a plant tumor disease caused by the specific action of the bacteriumAgrobacterium tumefaciens. In the current literature its host range is not clearly defined or is thought to be restricted to the dicotyledonous class of the angiosperms.

Evolution of DNA content in higher plants

Abstract: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Range of Variability of DNA Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 DNA Variation in Higher Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Gymnosperms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Angiosperms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Mechanisms of Change in DNA Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Cellular and Organismic Correlations with DNA Content . . . . . . . . . . . . . . . . . . . . . . . . 40 Functions of DNA Sequences Duplicated or Deleted during Evolution . . . . . . . . . . . . . 41 Prospects for Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

The use of vegetation in assessing the productivity of forest lands

Abstract: The basic principles in the use of vegetation types as indicators on forest lands are enumerated and discussed. (1) Vegetation reflects the sum of all the elements of the environment which are important to plants. (2) The species with highest competitive powers are the best indicators. (3) Forests consist of superimposed groups (“unions”) which occur in different combinations ovethe landscape. (4) Each union is sensitive to certain special aspects of environment. (5) Many characters of vegetation have potential significance as ecologic indicators. (6) Types of environment (“habitat types”) are the most basic ecologic units of landscapes.

Morphology and nutrition of the colonial green algaScenedesmus: 80 years later

Abstract: This paper provides an overview of polymorphism in the colonial green alga,Scenedesmus, since discovery of this phenomenon over eighty years ago. Evidence is presented showing that the genus, as now generally considered, can be naturally sub-divided into two distinct groups which may be considered as separate genera. The extent of morphological variability in each group is discussed with particular attention given to the better-known, spine-bearing strains. Problems created by inclusion of both stable and unstable strains in the same taxon, as well as the complexity possible when variation in wall ornamentation is superimposed on colony-unicell transformations, are discussed. Data are presented showing that morphological type can be manipulated at will in some strains by careful control of nutrients. Experiments involving field incubations and laboratory studies using river water as a culture medium indicate that natural nutrient levels can regulate morphology and that polymorphic strains may be useful in providing assay organisms for assessment of water quality. Suggestions are offered as to how polymorphic strains, which have been ignored in all monographs to date, can be incorporated into a workable taxonomic scheme.

Bacterial leaf nodule symbiosis in angiosperms with emphasis on Rubiaceae and Myrsinaceae

Abstract: Over 400 species of three genera of Rubiaceae and one genus of Myrsinaceae reportedly have bacterial leaf nodules. Light and/or electron microscope studies of a few species have shown that bacteria exist in spaces within buds filled with mucilage secreted by glands. These bacteria enter substomatal chambers (Rubiaceae) or marginal hydathodes (Myrsinaceae) and establish short-lived colonies, in intercellular spaces, that die out almost before full leaf expansion. Bacteria occur in seeds between endosperm and embryo, but only two studies have followed bacteria into flowers and ovules. Previous work on the physical relations of bacteria and host plants is discussed critically. Reviewing work done on isolation and identification of presumed endophytes leads to the conclusion that there is no agreement whether one or several bacterial taxa are the endophyte, and no unambiguous identifications, although four genera are suggested as possibilities. Nitrogen fixation was considered as the bacterial contribution until quite recently, but a review of such studies reveals that fixation has been detected almost exclusively in isolated presumed endophytes, whereas almost all studies involving the bacterium in intact leaves have failed to detect nitrogen fixation. Studies of particular substances (besides combined nitrogen) contributed by the endophyte have been inconclusive, although the most recent works suggest that cytokinins are involved. Host plants lacking the endophyte have been reportedly produced many times, either spontaneously or by seed treatment. Such “cripples”, used for several aspects of symbiosis study, frequently revert to a nodulated condition, and a more reliable method of producing them is needed. Tissue culture may offer the best potential, but this approach has not yet produced whole bacteria-free plants. A proposed scheme for the evolution of the symbiosis suggests that a variety of bacteria entered buds first, and only in rare instances were compatible with the host bud mucilage. In a few of these cases, specific bacteria, compatible with the microenvironment, contributed a useful substance to the host, and bud mucilage and those bacteria co-evolved until large numbers of bacteria thrived in the buds. Nodules may have resulted from accidental entry of bacteria into leaves, with the possibility that some host plant nodules are merely pathogenic responses, whereas in others the bacteria are beneficial and further selection has resulted in numerous, regularly produced nodules. This review deals with taxonomy of host plants and endophytes, morphology of the symbiosis, its physiology, and speculation on the evolution of the symbiosis.

The inflorescence of Carex and related genera

Abstract: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Subgenera and Inflorescence Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 The Female Flower and Spikelet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 The Male Flower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Inflorescence Abnormalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Ontogenetic Interpretation of the Inflorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Evolution of the Inflorescence in the Cariceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Origin of the Inflorescence of the Cariceae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

The morphological interpretation of epiascidiate leaves —An historical perspective—

Abstract: Epiascidiate leaves are those foliar organs whose adaxial (ventral) side is the inside of a tube. Such tubular leaves are found in Nepenthaceae, Sarraceniaceae, Cephalotaceae, and Lentibulariaceae. Throughout botanical history these leaves have received considerable attention because of their bizarre morphology and problems of interpretation. This paper documents the attempts of the last 150 years to correctly understand their organographic nature. All epiascidiate foliar organs are structurally similar in their early ontogeny, each forms a distinctive adaxial outgrowth (Querzone), and the diverse morphologies of the mature organs seem to be modifications upon a similar primordial ground plan. Typologically these leaves are directly related to peltate leaves and phyllodes (non-petiolar,sensu Boke). Except for certain, highly speculative,de novo theories, such as the “foliar runner” theory of Croizat, all misinterpretations of the nature of epiascidiate leaves are directly attribuable to earlier errors in ascertaining the organography of typologically related leaf forms. Accordingly, the sympodial tubular leaf (Roth) is rejected, as is the petiolar nature of tubular leaves (de Candolle). The typological relationships of these leaves to unifacial foliar organs (Troll) seems well substantiated from both an organographic and a histogenetic viewpoint. The peltate carpel theory (Celakovský; Troll) is, in reality, an epiascidiate carpel theory. The idea of a fundamentally tubular carpel seems correct from both a typological and phylogenetic standpoint. To comprehend the various contradictory interpretations which have been used to explain morphologically complex problems, as well as to understand the genesis of morphological theories, it is necessary to acquire an accurate historical perspective of the subject.