摘要:

Pollen presenters are specific floral structures, other than anthers, from which pollen is distributed for cross fertilization between flowers. They occur in only five families of monocotyledons and 20 families of the dicotyledons. Presenters in 15 families are described here. In the largest plant family (Asteraceae) all taxa have pollen presenters, while in others (e.g. Myrtaceae) they occur in only some species in a few genera. Most presenters are associated with the gynoecium and there is a wide range of forms involving hairs or outgrowths of the stylar tissue. Despite the placement of self pollen close to the stigma most taxa are outcrossing and avoid self fertilization by protandry, with the stigma being covered at anthesis, or by precise placement of pollen so that is does not contact the stigma. Likely selective advantages in the development of pollen presenters include greater accuracy in pollen transfer than in the normal anther to stigma movement and avoidance of interference between male and female organs in the flower. In some groups there is enhanced ability for female choice because effective pollen delivery enables a choice from among many pollen grains, while in others pollen presenters enhance male reproductive success. Study of the pollination biology of plants requires a knowledge of which plants have pollen presenters and a full understanding of the structures in the flower which are associated with the pollen presentation action.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01777.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

A multidisciplinary investigation of the eight annual taxa ofBromussect.Geneathroughout their total ranges has brought a fresh insight into their evolutionary pathways. These species, mainly in southwest Asia and the Mediterranean, are still actively in the process of speciation and their study illuminates evolutionary processes in annual grasses as a whole. Following a discussion ofGeneafeatures, a list of ancestral and derived characters in the group is presented. The recent emergence of a multiplicity of niches is probably the reason for the rapid emergence of many new kinds of plants in sect.Genea.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01778.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Many leaf characters are considered in the taxonomy ofCrataegusin Europe, and several have been used in studies of the extent of hybridization in populations of northwest Europe. In such analyses it is assumed that the environmental component of phenotypic variation in such characters is insignificant. We tested this assumption by analysing the variation in the size and shape of leaves borne on clone cuttings ofCrataegus monogynamaintained under identical conditions apart from the availability of soil nutrients. The resulting variation among leaves from this single genotype was as great as that observed previously across populations. Furthermore, although most of this variation could not be explained, a part could be attributed to differences in nutrient availability; of nine leaf characters investigated, eight showed significant variation due to this source, and in seven, the variation covaried significantly with nutrient level. The systematic implications of this are briefly explored.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01779.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Fruit development and structure of three southern African species ofApodyteswere examined by light and scanning electron microscopy. These areA. dimidiataE. Meyer ex Arn. subsp.dimidiataand two undescribed species designatedApodytessp. nov. A and B. Fruits are unilaterally developed drupes, ellipsoid and somewhat compressed laterally, with a large succulent appendage. Appendages ofA. dimidiataandApodytessp. nov. A are predominantly red, whereas those ofApodytessp. nov. B are a pale translucent green. In all three species the appendages turn black in old fruit. The exocarp is uniseriate and develops solely from the outer epidermis of the ovary wall. The mesocarp is partly parenchymatous, with vascular bundles and cells containing druse crystals of calcium oxalate, and partly lignified (= stone). The uniseriate endocarps. sir.develops from the inner epidermis of the ovary wall. In a sense the fruit ofApodytesis a composite of parts comparable to a nut (alternatively an achene) and a fleshy drupe. The drupaceous part (fleshy appendage) is a derived structure which develops from the sterile carpel of a reduced locule. We suggest that the fleshy appendage originates as an indicator of seed/fruit maturity, and to attract avian dispersers. Limited field observations support the idea that the red/black appendages ofA. dimidiataandApodytessp. nov. A also serve as an edible reward for birds. Dispersal of fruit ofApodytessp. nov. B, with its rather inconspicuously coloured appendage, may be dependent on a specialized fruit/frugivore relationship.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01780.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The nameCytisus proliferusL.f. is here considered perfectly acceptable and should not be replaced byCytisus proliferL.f. One specimen from The Natural History Museum, London is confirmed as the lectotype ofCytisus proliferusL.f. Two specimens from the collection of the Swiss botanist Hermann Christ from the Main Herbarium of the Zurich Botanical Garden were selected as lectotypes forCytisus proliferusL.f. var.canariaeH. Christ andCytisus proliferusL.f. var.palmensisH. Christ. The nameCytisus proliferusKit. is typified and a specimen from Paul Kitaibel's collection at the Botanical Department of the Hungarian Natural History Museum is assigned as its lectotype.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01781.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Fungal fruiting bodies ignored in earlier palynological investigations of the Subathu and Dagshai Formations have been studied from sediments exposed in the Dadahu Jamtah area, Sirmaur district, Himachal Pradesh. Taxa belonging to the generaNotothyrites, Asterothyrites, Parmathyrites, PhragmothyrilesandMicrothyriaciteshave been identified. These fossils are comparable with taxa reported from many Early Tertiary assemblages from different parts of the country and indicate a warm and humid climate.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01782.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1994.tb01783.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY