Stephen Blackmore

EMBRYOPHYTE SPORE WALLS: ORIGIN, DEVELOPMENT, AND HOMOLOGIES

LITERATURE CITED COLLESS. D. H . 1985. O n “character” and related terms. Syst. Zool. 34: 229-233. DUARTE RODRIGUES, P. 1986. On the term character. Syst. Zool. 35: 140-141. FARRIS, J. S. 1970. Methods for computing Wagner trees. Syst. Zool. 19: 83-92. FARRIS, J. S., A. G. KLUGE, and M. J. ECKARDT. 1970. A numerical approach to phylogenetic FELSENSTEIN, J. 1985. Confidence limits on phylogenies: An approach using the bootstrap. EvoluFINK, W. L. 1986. Microcomputers and phylogenetic analysis. Science 234: 1135-1139. FOULDS, L. R., AND R. L. GRAHAM. 1982. The Steiner problem in phylogeny is NP-complete. GHISELIN, M. T. 1984. “Definitions,” “characters,” and other equivocal terms. Syst. Zool. 33: LUCKOW, M., AND R. A. PIMENTEL. 1985. An empirical comparison of numerical Wagner comLUNDBERG, J. G. 1972. Wagner networks and ancestors. Syst. Zool. 18: 1-32. MADDISON, W. P., M. J. DONOGHUE, and D. R. MADDISON. 1984. Outgroup analysis and parMICKEVICH, M. F. 1982. Transformation series analysis. Syst. Zool. 31: 461-478. NELSON, G. 1978. Ontogeny, phylogeny, paleontology, and the biogenetic law. Syst. Zool. 27: PENNY, D., AND M. D. HENDY. 1985. Testing methods of evolutionary tree construction. Cladistics PLATNICK, N. I. 1977. Cladograms, phylogenetic trees, and hypothesis testing. Syst. Zool. 26: SOKAL, R. R., AND P. H. A. SNEATH. 1963. Principles of numerical taxonomy. Freeman, San systematics. Syst. Zool. 19: 172-191. tion 39: 783-791.

Pollen wall morphogenesis in Tragopogon porrifolius L. (Compositae: Lactuceae) and its taxonomic significance

Abstract Pollen development in Tragopogon porrifolius has been studied in the scanning electron microscope to establish the origin of taxonomically significant features. As in other members of the tribe recently investigated the echinolophate condition is shown to result from differential deposition of the tetrad callose wall and, subsequently, of primexine. Tragopogon differs from other Lactuceae in the absence of tectum and columellae in the lacunae, this also appears to be the result of differential primexine deposition. The development of onci and their extrusion at the apertures are described. The contribution of developmental studies of pollen grains to systematics is discussed.

Palynology of subtribe scorzonerinae (compositae: lactuceae) and its taxonomic significance

Abstract Pollen samples of c. 130 species from all seven genera of subtribe Scorzonerinae have so far been examined by light, scanning electron microscopy and with transmission electron microscopy for selected examples. The pollen grains are 3- (rarely 2-, occasionally 4-) colpororate and share a distinctive exine stratification and aperture configuration. Echinate and echinolophate pollen grains occur in the subtribe. Seven pollen types, distinguished primarily by the number and position of their lacunae, are described. A cladistic analysis of the pollen characters indicates the probable relationships between the genera. The results support the status, given by some authors, of Epilasia and Pterachaenia as genera distinct from Scorzonera and Geropogon from Tragopogon.

Observations on the substructural organisation of the exine in Fagus sylvatica L. (Fagaceae) and Scorzonera hispanica L. (Compositae: Lactuceae)

Abstract Treatment of acetolysed pollen grains with potassium permanganate exposes substructures by removing part of the exine. New surface details are exposed between tectal and infratectal elements. In sectioned pollen grains ectexinous components including columellae and the tectum are eventually reduced to a system of spaces delimited by a layer which is resistant to the treatment. This is referred to as a “boundary layer” and is composed of a granular or fibrillar meshwork. Results from investigations of Fagus sylvatica and Scorzonera hispanica are compared with earlier studies of exine dissolution and a new hypothesis for exine substructure is presented. In this interpretation the boundary layer is conceived as delimiting areas which are receptive to sporopollenin during early development and so define ectexine stratification and ornamentation. Subsequent addition of tapetal or microsporal sporopollenin masks the boundary layer to a greater or lesser extent in different taxa. The ability to reveal the boundary layer in mature pollen may provide ontogenetically significant information concerning the organisation of pollen walls.

Cosmos pollen ontogeny: A scanning electron microscope study

SummaryOntogenetic data concerning pollen not only clarifies the mode of deposition of the elaborate walls but has considerable functional and taxonomic relevance. Hitherto such studies have used optical or transmission electron microscopy but here a recently devised preparative technique has enabled pollen development inCosmos bipinnatus to be studied using the scanning electron microscope. The technique involves freeze-fracturing of osmium fixed, cryoprotected anthers, maceration in dilute osmium tetroxide, critical point drying, sputter coating and examination. The processes of pollen wall development can then be observed in three dimensions, an important aid to understanding the spatial relationships involved in the determination of ornamentation and apertures. Details of the pollen and tapetum are described at various stages between meiosis and anthesis. A close conformity is demonstrated between the results obtained and those of earlier transmission electron microscopic studies of the same and related species although very different interpretations are made.

On the terminology, origins and functions of caveate pollen in compositae

The terminology applied to caveate pollen in the Compositae is reviewed. The term cavea (plural: caveae) is recommended in preference to cavus, the plural of which should be cavi although this has not been used in the literature. Caveae are interpreted as being potentially present in all Compositae since all the members of the family studied possess them during their early developmental stages. In some taxa the caveae are well developed in the mature pollen and function primarily as harmomegathia whilst in others the caveae are obscured by the later development of columellae which limit or prevent the harmomegathic function.

A functional interpretation ofLactuceae (Compositae) pollen

Pollen morphology and ultrastructure inLactuceae pollen is considered in relation to the accomodation of volume changes, pollination biology and exine-held substances. Echinate pollen grains, such as those ofCatananche, are shown to accomodate volume changes by folding along the colpi and possibly by volume changes in the cavea. The different patterns of echinolophate pollen respond in different ways. Folding along the colpi is important inScorzonera andTragopogon and to a limited extent inCichorium andEpilasia whilst inScolymus the colpi are almost immobilized. Movements of the lacunar floors take over the harmomegathic function to compensate for lack of colpus mobility. Bulging of the intine at the apertures and changes in the size of the cavea may account for part of the volume change accomodated in any pollen type. Echinolophate pollen is interpreted as being a superior means of regulating volume changes with the most economical and mechanically efficient use of wall material which has evolved independently in several tribes ofCompositae.

Scanning electron microscopy of chloroplast ultrastructure

Abstract A range of fracturing and sectioning techniques are now available which permit intracellular structures to be observed in the scanning electron microscope. One such technique, based on the method of Tanaka (1981), has been used to study chloroplast ultrastructure in Japan laurel, Aucuba japonica. Small pieces of leaves were fixed, fractured whilst frozen and transferred to a dilute solution of osmium tetroxide in which cytoplasmic maceration took place. Specimens were dehydrated, critical point dried and examined was required to remove the stroma from fractured chloroplasts. Following this treatment details of the chloroplast envelope, frets, grana and plastoglobuli could be observed. The results were compared with conventionally prepared thin sections examined in the transmission electron microscope and with the three dimensional reconstructions described in the literature.

Phylogenetic trends in the Alismatales with reference to pollen grains

Abstract The pollen morphology of Butomaceae, Limnocharitaceae and Alismataceae, the three families comprising the Alismatales, was studied using light and scanning electron microscopy. Pollen grains of the monotypic Butomaceae are monosulcate and boat‐shaped, those of Limnocharitaceae have 4–10 ill‐defined, fimbriate, globally distributed pores, and those of most Alismataceae are pantoporate and spheroidal, or rounded polyhedral. However, Alisma oligococcum has unusual 2‐porate, lens‐shaped pollen grains, indicating an isolated position in the family so far as apertures are concerned. Pollen morphological characters of the order were analysed using cladistic methods and a hypothesis for pollen evolution in the Alismatales is presented. Monosulcate pollen is clearly primitive in the order, as amongst monocotyledons in general, whilst derived pollen grains possess higher numbers of pores. Fimbriate aperture margins, areas of circumporal ornamentation and sunken apertures are also considered derived. The ge...

Palynology and systematics of morinaceae

Pollen grains from all thirteen species of the three genera to be recognised in a forthcoming revision of the Morinaceae, Acanthocalyx, Cryptothladia and Morina, have been investigated by light and scanning electron microscopy. Fresh pollen of M. longifolia has also been studied by light, scanning electron and transmission electron microscopy. Three main pollen types are described and a key provided for their identification. Each pollen type occurs throughout a genus. Further division of two of these pollen types enables groups of species to be recognised. Functional aspects of the pollen are discussed, especially their unique pre-germinative processes. A cladistic analysis of pollen characters provides a hypothesis for their evalution and supports the classification proposed in the recent revision.