摘要:

EE WARDS, D., KENRICK, P.&CARLUCCIO, L. M., 1988.A reconsideration of cf.P lophyton princeps(Croft&Lang, 1942), a zosterophyll widespread in the Lower Old Rt 1 Sandstone of South Wales.The Lower Devonian plant from Llanover Quarry, Gwent, cal ed cf.Psilophyton princeps, is shown to be a zosterophyll and placed in a new genus. It comprises an ere t planar pseudomonopodial and isotomously branching system of spiny axes with subaxillary pre ections (axillary tubercles) with circinate tips, sometimes replaced by a downwardly directed, spiring, branching axis. Its xylem, strap‐shaped in cross‐section and exarch, is composed of directly and ndirectly connected annular thickenings. An extended distal fertile zone consists of axes with spot ingia in two opposite or sub‐opposite rows. Each sporangium comprises two equal valves, ellip'ical to reniform in face view, and is held upright on a short curved stalk. Dehiscence is around the convex margin which is bordered by a narrow strip of thickening. The Welsh plants are comp ired with other zosterophylls and appear closest toSawdonia ornataexcept that they possess sub‐axillay branches and lack the characteristic dark‐tipped spines. Detailed analysis of coalified mater: and the distribution and fabric of pyrite in permineralizations shows that the original structure of the tracheids was similar to that inGosslingiaand most other zosterophylls, and that the taphonomic processes, with lignified walls preserved as coalified layers and softer tissues replaced by pyrite, were also broadly the same. Permineralizations in pyrite and limonite allow an evaluation of the effects of oxidation of pyrite on original cell

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb01723.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

GAHAN, P. B., 1989.How stable are cambial initials?An autoradiographic study of the incorporation of [3H] thymidine into nuclei of cambial initials in stems ofLycopersicon esculentumhas permitted the identification of subpopulations of cambial cells with differing rates of turnover. It is proposed that the true cambial initial cells have a very low rate of turnover and merely provide a population of daughter cells which are the readily identifiable, frequently dividing cambial cells.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb01724.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

NAIR, M. N. B. AND MOHAN RAM, H. Y., 1989.Vestured pits and vestured vessel member walls in some Indian dicotyledonous woods.The woods of 144 taxa belonging to 38 families of angiosperms were examined for vestured pits and vestured vessel member walls using scanning electron microscopy. Vestured pits are present in 66 taxa (belonging to ten families) and vestured vessel member walls occur in only six taxa (belonging to three families). In Ehretiaceae and Euphorbiaceae vestures are present only in certain vessel members. InWrighlia tinctoria, perforation plates containing vestures have been observed in addition to the presence of vestured pits. A classification of vestured pits based on their morphology and distribution is proposed by us. In all the types of vestured pits, vestures are present on the margin of the outer pit aperture or on the pit chamber wall. Occasionally, they are present in the pit canal, on the margin and in the vicinity of the inner pit aperture and rarely over the inner walls of the vessel members. The functions of vestured pits are not clear, although several suggestions are made. Whether or not these structures affect wood processing is not presently understood. It appears that vestured pits and vestured vessel member walls have diagnostic rather than phylogenetic value.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb01725.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

NIC LUGHADHA, E. M.&PARNELL, J. A. N., 1989.Heterostyly and gene‐flow inMenyanthes trifoliataL. (Menyanthaceae).Menyanthes trifoliatais shown to be a self‐incompatible heterostylous species with a suite of associated pollen and gynoecium dimorphisms. These features may promote legitimate pollination. Analysis of a natural population showed substantial pollen inviability, a preponderance of illegitimate pollen on stigmas and a possible asymmetry of pollen flow. Mean pollen travel was estimated as 2.6 m by counting legitimate grains on stigmas whose distance from the nearest source of legitimate pollen was known. Direct field and laboratory measurement indicated mean seed travel of<0.2m. The density of flowering spikes varied greatly within the studied colony ofMenyanthes, with a mean of 0.93 m‐2. Using suitable corrections the genetically effective density was estimated as between 0.04 and 4.4 m‐2. Crossing experiments indicated thatMenyanthesis fully outcrossed (r=1). The neighbourhood area was estimated as 10–15 m2while neighbourhood size ranged from less than one to sixty‐five. Some published neighbourhood estimates are revised with the results forMenyanthesbeing at the lower end of the range. If the genetically effective density were estimated more accurately, neighbourhood estimates would likely be lower still. It is concluded that what is generally referred to as a population ofMenyanthes, may actually represent many evoluti

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb01726.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

RICE, E. L., 1989.A statistical morphological analysis and taxonomic revision of the genusXiphophora(Fucaceae).Xiphophorais a brown seaweed endemic to the cool temperature rocky shores of Australia and New Zealand. The two species,X. chondrophyllaandX. gladiatahave previously been separated by morphological criteria. However, the differences betweeen them in these characters were largely size‐related, resulting in taxonomic confusion. In particular, the presence ofX. gladiatain New Zealand has been disputed. In this study, a series of discriminant function analyses were performed, based on a suite of morphological characters collected from each species throughout a major portion of their geographic ranges. The results show conclusively that the present taxonomyof Xiphophorais untenable. This genus is composed of two species, but these are distributed latitudinally (either side of the 40oS parallel). Each species contains two allopatric subspecies; one in Australia and the other in New Zealand. A formal taxonomic revision of the genus is presente

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1989.tb01727.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY