摘要:

Pachycormus discolor, an arborescent desert perennial endemic to Baja California, has small, pinnately compound, hypostomatic, bifacial leaves produced on short shoots and photosynthetic stem phelloderm covered by exfoliating translucent phellem. Tightly packed laminal palisade cells are filled with tannins and lack chloroplasts. Spongy mesophyll is the major photosynthetic tissue. Leaves possess unicellular trichomes with secondary walls and uniseriate trichomes with glandular heads. Schizogenous resin ducts occur in primary phloem of stems, leaves and roots as well as all living tissues of the bark. Developmental studies reveal that initiation and differentiation of foliar primordia resembles that of other dicotyledons except that tannin cells and secretory ducts arise precociously. Primary vasculature is an open sympodial system with three principal traces diverging toward each foliar primordium. The wood is highly specialized and comprises mostly unlignified cells packed with starch grains. Thick bark is mainly produced as annual layers of secondary phloem marked by a ring of secretory ducts each surrounded by tannin cells. The possible adaptive significance of these unusual anatomical features is discussed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1981.tb00351.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The morphology of individuals of mixed natural populations of three species ofAlopecurus, A. pratensis, A. genicularsandA. arundinaceus, is described. It is suggested that plants morphologically intermediate between the parental species are hybrids or of hybrid origin. Hybridization occurs more readily betweenA. pratensisandA. arundinaceusthan betweenA. pratensisandA. geniculate, since intermediate forms were recovered from all mixed populations ofA. pratensisandA. arundinaceus.The intermediate forms occur only in a few populations ofA. pratensisandA. genicularswhere an appropriate habitat is available. Evidence of backcrossing and therefore introgression comes from the continuum of intermediate forms that exists between the species. Scatter diagrams for individual populations show distinct differences in the degree of introgression. Observations on artificially produced hybrids are similar to those on naturally occurring hybrids.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1981.tb00352.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The meiotic behaviour of plants from mixed populations ofAlopecurus pratensis×A. geniculatusand ofA. pratensis×A. arundinaceus(2n= 4×(= 28) is reported together with observations on some artificially produced hybrids. This meiotic behaviour is correlated with the degree of hybridity as shown by the hybrid index values of the plant. InA. pratensis×A. geniculatushybrids there are marked differences between populations in the degree of meiotic disturbance and in one population there was an almost complete breakdown of meiosis.Alopecurus pratensis×A. arundinaceushybrids show fairly regular meiotic pairing but in most plants there are a few univalent chromosomes at metaphase I. Artificially produced hybrids ofA. pratensis×A. aequalisgave meiotic configurations that suggest that the genomes of the parent species are very similar. Taken together with the results from artificially produced hybrids ofA. pratensis × A. geniculatus, it is suggested that bivalent‐promoting mechanisms reduce multivalent formation both in the species and the hybrids. The interaction of different genotypes involved in the control of meiosis may account for the variation in meiotic behaviour in the different populations of hybrids. Pollen fertility is reduced in most populations of hybrids and likely to be an important factor permitting introgressive hybri

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1981.tb00353.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Morphological evidence suggests thatLimnobiumandHydrotnystriashould be maintained as two distinct genera. Taxonomic descriptions of the genera and species are provided. The geographical distibution of the two genera is given and the combinationHydrotnystria laevigata(Humb.&Bonpl. ex Willd.) Diaz‐Miranda&Philcox is presente

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1981.tb00354.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The botanical career of Nathaniel Wallich is followed; his collecting activities in Asia enumerated, and the final disposition of his huge herbarium, largely the property of the Honourable East India Company, is given. His relationship with numerous eminent contemporary botanists, and particularly with the de Candolles of Geneva, is described, together with the role that each played in assisting Wallich to work up his material.A full list of the works used in the composition of this paper is given in an Appendix rather than following the usual citation convention. Copies of the correspondence between Wallich and the de Candolles of Geneva are available on microfiche.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1981.tb00355.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY