摘要:

New collections of microphyllous plants identical to those described by Halle almost 60 years ago and identified by him asDrepanophycus spinaeformisGöpp., 1852 have been made from the Emsian Xujiachong Formation, near Qujing City, eastern Yunnan Province. New information relates to orientation of leaves, epidermal and xylem anatomy, vegetative and fertile leafy shoots with roots and sporangia. The latter, dehiscing distally into two equal valves diat are elliptical to circular in face view, are attached directly to the stem by short stalks. They show no consistent relationship to leaves and are supplied by a separate vascular trace much wider than that to leaves. Detailed comparison is made with the cosmopolitan and stratigraphically long‐ranging speciesD. spinaeformis.The Chinese specimens can be distinguished on leaf orientation, their anomocytic stomata and sporangial characters, although the latter remain conjectural inD. spinaeformis,and are therefore placed in a new speciesDrepanophycus qujingensis.Hypotheses relating to cooksonioids, zosterophylls and the origin of the lycopsids are reviewed and the phylogenetic position of the new taxon assessed. It is concluded that it has greatest affinity withAstewxylon mackiei,and that both exhibit the kind of fertile organization that might be anticipated in the ancestors of the lycopsi

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00468.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Localization of the stamens can be approached by a preliminary distinction between two characters, oligomery and polymery, occurring in two different groups of taxa, respectively the oligomerous complex and the polymerous complex. Oligomery is described by four character states standing in a close semophyletic relationship: diplostemony, obdiplostemony, haplostemony and obhaplostemony. Each character state is analysed for its distribution and systematic value. Diplostemony is the synapomorphic character state for the oligomerous line and has arisen once from a polymerous ancestor or in parallel in different lines. Obdiplostemony arises ontogenetically in three different ways. Loss of one whorl leads either to obhaplostemony, or haplostemony; both character states are believed to represent evolutionary steps of no‐return. Secondary increases and reductions of the stamens within a whorl are seen as expressions of the intrinsic variability of the character states and should not be homologized with them. Stamen numbers can be increased by the building‐up of complex primordia or by secondary receptacular growth. Reductions of stamens affect one or two whorls of stamens and are caused by lack of space, interactions with the gynoecium and zygomorphy. The distribution of the different character states of oligomery is presented on Dahlgrenograms and the androecia of a number of families and their relationships are discussed. The interactions between oligomery and polymery are analysed as guidelines for a global phylogeny of the Magnolia

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00469.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A large euchromatic supernumerary segment (ss) occurs at a high frequency in a natural population ofScilla autumnalisfrom the west of the Iberian Peninsula. Mother‐offspring analyses have shown random pollination of all bulbs lacking the extra segment but non‐random pollination of some bulbs carrying it. With a single exception, ss transmission appeared to be Mendelian through the eggs of heterozygous bulbs, which was consistent with results of controlled crosses. An analysis of the effects of this ss on some female fitness components demonstrated significant differences between genotypes for mean seed weight. Heterozygous bulbs yielded significantly heavier seeds than standard homozygous bulbs, and slightly (but not significantly) heavier seeds than segment homozygotes. No trade‐off was observed between seed number and seed size in this population. In heterozygotes there was a surprising positive correlation between fruit fertility (number of seeds per fruit) and seed weight. These results are discussed in relation to the maintenance of the segment in natural popula

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY