摘要:

This is d study of the reproductive biology of wild gametophytes ofEquisetum arvenseL.,E. fluviatileL., andE. palustreL., which form extensive populations during the summer months on previously inundated bare mud along the margins of reservoirs and lakes in Northern England and Wales. The garnetophytes have all the characteristics of pioneer species: they rapidly attain sexual maturity and are adversely affected by competition. Early in the summer mixtures of male and female gametophytes are produced. The former are smaller and their frequency (which is always less) diminishes throughout the season as a result of bryophytic competition. The rarity of bisexual, initially female, gametophytes, in wild populations is related to the absence of metabolite accumulation which mediates this change in rulture. Significantly different sex ratios between populations and species underlines the labile nature of the sex‐determining mechanism inEquisetum. The high frequency of females bearing sporophytes indicates that intergarnetophytic fertilization is highly effective in nature. Absence of any correlation between the incidence of fertilized females and the proportions of males, in conjunction with a consideration of the male gamete dispersal distance, suggests that sporophyte formation is restricted by the availability of ripe archegonia. Sexual reproduction inEquisetumis probably limited by the narrow range of conditions under which gametophytes can become established rather than availability of water for fertilization. The majority of females, which bear one sporophyte, are smaller than unfertilized or polyembryonic females. Their small size results from nutrient demands and allelopathic compounds from the sporophytes which also probably prevent the establishment of gametophytes within mature stands of the parent species. Correlations between female diameters and frequencies of males suggest that gametophytes are more likely to produce archegonia under favourable conditions. The natural reproductive biology ofEquisetumis in accord with predictions based on an understanding of the mechanism of sex determination in axenic culture. Several striking parallels between sexuality inEquisetumand dioecious angiosperms are revealed.The absence of winter flooding at two of the gametophyte sites led to the establishment of mature rtandsof Equisetum, which produced cones after 3–4 years; two hybrids,E. fluviatile×E. arvenseandE. fluviatile×E. palustre, were det

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01655.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Basipetal to the shoot apex, a procambial ring with parenchymatous gaps is present. The protoxylem poles are endarrh in both the ectophloic siphonostele and the collateral vascular bundle which comprises the leaf trace. Each leaf trace has an anastomosing system of protoxylem poles that decreases in number basipetally from five to three to two. Differentiation of the leaf trace procambium and protoxylem is bidirectional, that is the differentiation first occurs near the base of the leaf and acropetally in the leaf and basipetally in the stem. Then a fascicular cambium differentiates betweem the primary xylem and phloem in the leaf. This vascular cambium which is also present in the stem is unidirectional and only produces secondary xylem centripetally. Limited secondary growth also occurs in roots. Medullary tracheids when present are longitudinally continuous with the vascular system. The stele of the stem is interpretated as a sympodium of leaf traces and the pith is considered to be fundamental tissue enclosed by the anastomosing of leaf traces.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01656.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The composition and affinities of the bipinnateAcaciaseriesPulchellaeBentham are examined in the light of evidence from studies of gross morphology, seedling morphology, pollen morphology and seed chemistry.Acacia mitchellii, the only non‐Western Australian species, is atypical and should be relocated in sectionVninerveaVassal. The remaining 27 species (thePulchellae sensu lato) comprise a coherent group of 21 species (thePulchellae sensu stricto) and six less closely related ones. These 27 species appear unrelated to seriesBotrycephalaeBentham. Some affinities exist with phyllodinous groups, especially seriesUninervesandContinua

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01657.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The variability in theAcacia niloticacomplex is explained in terms of hybridization betweenA. niloticasubsp.indicaandA. niloticasubsp.hemispherica. This is substantiated by the study of phenolic constituents, pollen fertility and intra‐plant fruit variability. The hybrid populations may backcross withA. niloticasubsp.indicaandA. niloticasubsp.hemisphericaproducing plants similar toA. niloticasubsp.adstringensandA. niloticasubsp.subalatarespectively. The role of humans in directly and indirectly distributing the seeds of hybrid plants over vast areas and in creating the disturbed habitats suitable for plants of hybrid origin is discussed. Phenolic constituents ofA. niloticasubsp.hemisphericaandA. niloticasubsp.leiocarpaare shown to be distinctive. Probable hybridization betweenA. niloticasubsp.indicaandA. niloticasubsp.cupressiformisis also discusse

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01658.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Data for the chemical composition of the gum exudates fromAcacia acradenia, A. aneura, A. acuminata, A. beauverdiana, A. coolgardiensis, A. kempeana, A. microneura, A. resinomarginea, A. stereophyllaandA. torulosaare presented. Comparisons with the data reported previously for other species of the seriesJuliflorae, viz. A. auriculiformis, A. holosericea, A. leptostachya, A. mangiumandA. pubifoliaconfirm that the gums from this series have interesting combinations of chemical properties that are unusual inAcacia. The data do not offer much chemotaxonomic support for the groupings of theJulifloraesuggested by Bentham (1864). On the basis of their gross morphological features, the species under consideration are re‐grouped in a way that is also better supported chemicall

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01659.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The variation in chemical composition of 15 specimens of the gum exudate fromAcacia karrooHayne, obtained from four different African locations, has been investigated. The range of analytical values found (e.g., specific rotation + 36° to + 67°; uronic acid 10.3 to 18.1%; rhamnose 4 to 10%) reflect the well‐known variability of thisAcaciaspecies. The major analytical difference concerns the unusually wide range of molecular weights observed, i.e., 1.5 × 105to 48 × 105. The material of highest molecular weight, from trees infested with Cerambycid beetles, is consumed by bush‐babies (Gal

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01660.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1980.tb01655a.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY