摘要:

SUMMARYConclusions reached by Young(1981) concerning the evolutionary status of homoxyly in woody Angiosperms are biassed because the results of his analyses are based upon the silent acceptance of certain postulates and on assumptions emanating from such current but most probably untenable tenets. The phylogenetic history of the Angiosperms, if unravelled by alternative viewpoints and by,e.g., correlation studies yielding an “advancement index” (Sporne1982), and as substantiated by recent paleobotanical findings, most probably proceeded pleiorheithrically rather than monophyletically. The construction of cladograms starting from the postulation of a monophyletic ascent of the Magnoliophyta does not necessarily reflect the true evolutionary history of these Flowering Plants. In Young's cladistic analysis another difference between his adopted conventional viewpoints and alternative, dissentient ideas is that some or all of the supposedly apomorphic (i.e. newly acquired) character states need not have originated only once (as accepted and emphasised in his paper), but may well have arisen repeatedly and independently in two or in more parallel evolutionary lineages evolved from technically still gymnospermous ancestral forms and each terminating in some present‐day angiospermous assembly.The principal conclusion attained by Young,viz., that the incidence of homoxyly in arborescent Angiosperms is attributable to a secondary “loss” of the wood vessels by paedogenesis or otherwise, with corollary is partly based on cladistic analyses said to be leading to absurdities concerning wood vessel evolution, can be challenged because alternative starting points render these allegedly unacceptable evolutionary events highly plausible. At least some of the homoxylous primitive angiospermous taxa are early arrivals in the paleontological record, which is more compatible with an ancientry (i.e., plesiomorphy) of the character state of homoxyly in these taxa. Most if not all other conclusions emanating from Young's viewpoints are likewise to be rejected. Since prior to cladistic and other manipulations certain assumptions had been made and conventional ideas adopted as factual data, the ensuing evaluation of features and of character states is at least questionable and the qualifications of such characteristics as plesio‐ or as apomorphic is decidedly aprioristic. Parallelisms are not accounted for either, which means that the advent of vessel perforations need not have been a single evolutionary event but may have taken place repeatedly, some taxa never evolving beyond the level of homoxyly. For these and for other reasons one need not amend the generally held views concerning the primitive status of certain vessel‐less, arborescent Dicotyledons and the pleiomorphy of the character state of homoxyly in these taxa.This is another example of the inherent handicap in the application of cladistics that the results are to a large extent already aprioristically decided by the acceptance of tenets and “current” ideas and not by the cladistic methodology. One should first attempt to come to agreement as regards the evolutionary polarity of certain conditions and character states (i.e., the direction of phylogenetic advancement) before entering upon any form of cladistic analysis, lest cladistic approaches to Angiosperm phylogeny remain entirely futile because the results may prove

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01653.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYNavicula alterofasciata, spec. nov., described from post‐glacial lake sediments dating from the Preboreal up to and including the Atlanticum, is characterised by a fairly large, asymmetrical central area and a very fine, lightmicroscopically hardly discernible striation, and can provisionally best be referred to the sectionNaviculae subtillisimaeHusted

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01654.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYSpores of twenty species ofSpirogyrawere treated by acetolysis and viewed by scanning electron microscopy. The terms exo‐, meso‐ and endospore should be maintained and based on chemical composition. Exo‐ and endospore are cellulose and/or pectin containing membranes. The mesospore is acetolysis‐resistant and presumably contains sporopollenin.As basic pattern the spore wall inSpirogyrais composed of four layers: one exo‐ and endospore layer and two mesospore layers. The outer mesospore layer is mostly thin and hyaline, the inner layer thick and brown or yellow coloured and often sculptured. The germination suture is located in the inner mesospore layer. Some variations on this basic pattern were observed inSpirogyra bellis, S. cleveanaandS. majuscula. Details of mesospore sculpture were observed and some taxonomic implications are discussed.The observed basic pattern is assumed to be valid for theZygnemataceaea

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01655.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYHybrids ofV. arvensis(annual) andV. calaminaria(perennial) are regularly found on an open pit mine near Blankenrode (W. Germany). Morphological as well as karyological studies show that these hybrids represent different generations of selfing and/or backcrossing toV. calaminaria. The hybrids show a low tolerance to zinc.To study the gene flow the reproductive strategy of the parent species, their F1and F2hybrids was compared in a normal soil. The progeny of natural hybrids withV. calaminariawas investigated under zinc stress. The results show that F1and F2hybrids have a higher fitness thanV. calaminariaif both are grown in normal soil. This is caused by hybrid vigour and by a combination of the reproductive strategies of the parent species. When the progenies of hybrid plants are cultivated together withV. calaminariain soil with zinc added to it, no difference in reproductive capacity can be shown. Prolonged observations in the field have shown that the longevity of established hybrid plants is only slightly less than that of non‐hybrids.The observations are in accord with the assumption that a dynamic equilibrium exists between gene flow and selection. The consequences of this assumption for the genetic variation inV. calaminariaare discusse

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01656.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYTheory and practice of a sensitive infrared surface thermometer are dealt with. Several problems arising in the field use of this simple instrument are discussed and explained in detail. It is concluded that with the indicated precautions the instrument is operating at optimum reliability and accuracy. However, further increase in sensitivity will not yield higher accuracy.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01657.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYA survey is given of the syntaxonomic status and the internal differentiation of theJunco‐Menthetum longifoliae(androtundifoliae) and theCaricetum vulpinaein Europe. The following conclusions can be drawn:Junco‐Menthetum longifoliaeVegetation stands containingMentha longifoliado not belong to one association but are conglomerates i.e. mixtures of fragments.Mentha longifoliais not characteristic of theLolio‐Potentillionbut its epharmony is comparable to that of theFilipendulionspecies. The tall‐forb character of the conglomerates is conspicuous.ThePlantagineteaelement is of only minor importance under extensive grazing but increases with intensification of this factor.Junco‐Menthetum rotundifoliaeThe status of this association as a separate association is insufficiently founded.Caricetum vulpinaeTüxen 1947Contrary to the suggestion of Westhoff&VanLeeuwen(1966) and Westhoff&DenHeld(1969),Carex vulpinais not a character species of theLolio‐Potentillion. The preponderance ofMagnocaricionandPhragmiteteaspecies justifies the assignment of theCaricetum vulpinaeto these syntaxa.On a European scale no subassociations can be distinguished.The main internal differentiation is expressed by a gradual increase of the weight of theMolinio‐Arrhenathereteaand theScheuchzerio‐Cariceteaspecies as the dynamics of the hyd

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01658.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYNew material ofAutunia milleryensis(Renault) Krasser, an Early Permian representative of the pteridospermous family Peltaspermaceae, is described from the Lower Permian of the Nahe area, F.G.R.Sandrewia texanaMamay appears to be a synonym ofAutunia milleryensis. The new combinationsAutunia thomasiiandA. dzungaricaare introduced.Callipteris conferta(Sternberg) Brongniart is the sterile foliage attributed toAutunia milleryensis.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01659.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYFeatures of the self‐incompatibility system in the grasses are reviewed, and related to characteristics of the stigma and pollen tube growth. From a consideration of the existing data, a general hypothesis is advanced for the self‐incompatibility reaction, based upon the following propositions: (A) the pistil‐side incompatibility factors are proteins (probably glycoproteins) with lectin‐like properties present in the stigma surface secretions and in the transmitting tracts; (B) their binding specificities are such that they are complementary to sugar sequences or arrays displayed by wall carbohydrate in the growth zone of incompatible pollen tubes, but not complementary to those presented by the compatible tubes; (C) binding at the tip of an incompatible tube leads to a disruption of apical growth by preventing the dissociation of the polysaccharide content of the wall precursor bodies and interfering with the extension of polysaccharide microfibrils in the sub‐apical zone. The implications of the hypothesis are briefly discussed, and also its relevance to other gametophytic self‐incompatibil

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01660.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYPhytic acid, which makes up a large proportion of the phosphorus content ofPetuniapollen, undergoes only a very slow rate of degradation during the first two hours of germination. After two hours an active phytase (E.C.3.1.3.8) can be detected in pollen extracts and rapid degradation of phytic acid begins in the germinating pollen. Both the rapid degradation of the phytic acid and appearance of phytase activity can be prevented by cycloheximide, but not by cordycepin or actino‐mycin‐D. It is concluded that a pre‐existing, long‐lived m‐RNA in mature, ungerminated pollen is used during germination for the synthesis of phytase, which then catalyses rapid degradation of phytic acid. The product of this reaction is myoinositol, which is needed for pollen tube wall polysaccharide synthesis. The phytase synthesized during pollen germination has maximum activity at pH 5, does not require metal ions and is inhibited by fluoride and inorganic phosphate. The degradation of phytic acid and pollen tube elongation are retarded by inclusion in the medium of concentrations of phosphate inhibitory t

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01661.x

年代:1982

数据来源: WILEY

摘要:

SUMMARYIn all the species investigated the leaf epicuticular wax composition was found to be largely dependent on leaf age.In very young, still expanding, leaves characteristic patterns of aliphatic alcohols and non‐volatile aliphatic hydrocarbon homologues were found. The chain‐length distributions of the latter differ among the species and seem to be age dependent.In fully expanded leaves of all the investigated species leaf epicuticular wax synthesis continues during subsequent leaf life: the amount of wax per unit leaf area increases several fold and compounds not found in very young leaves are synthesized. In all the species investigated leaf ageing is accompanied by accumulation of a complex mixture of relatively short‐chain aliphatic hydrocarbon homologues.In fully expanded and older leaves of the fourHoyaspecies especially triterpenes and aliphatic hydrocarbons are synthesized. At these stages of leaf lifeseco‐nor‐triterpenols accumulate in the wax ofH. australisandH. crassipes. These substances are absent in young leaves. In comparable stages of leaf life methyl esters ofseco‐triterpene acids were found inH. australis, H. lacunosaandH. crassipes. These substances are also absent in young leaves. InH. keysii, on the contrary, free triterpenols were found to accumulate during leaf ageing. In the leaf wax of quite a different latex plant,Ficus benjamina, in addition to the aliphatics, only small amounts of triterpenols are present.Several observations have lead to the conclusion that theseco‐triterpenoids found in the leaf waxes are probably enzymatically formed by the plants themselves, and not photochemically nor by microbial phyllosp

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1982.tb01662.x

年代:1982

数据来源: WILEY