摘要:

Studies over a period of years have shown that two chytrids, morphologically very similar in the sporangial stage, occur on Asterionella formosa HasS. in certain lakes in the English Lake District. However, at dehiscence one is operculate and the other inoperculate. In the latter, part of the content of the sporangium flows out surrounded by a vesicle which soon bursts liberating the zoosporeS. It is now clear that both these species are included in the original description of the chytrid Rhizophydium planktonicum Canter. In so far as they are known, the life‐histories of these two chytrids are described and discussed in relation to previous records of parasites on Asterionella. The inoperculate chytrid becomes R.planktonicum Canter emend, and the operculate one is designated as a new species,Zygorhizidium affluens(syn. R.planktonicum Canter pro parte). It is this operculate species which is mainly responsible for the epidemics which occur on Asterionella in Windermere, Blelham Tarn and Esthwaite Water. The hyper‐parasiteRozellaparva sp.nov., is also described; it parasitizes sporangia and resting spores ofZ. Afflu

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1969.tb01970.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

This paper assembles and, so far as is possible without extended field and herbarium studies, examines critically the validity of records of marine and brackish‐water Chlorophyta and Xanthophyta for the western coast of tropical Africa. The whole mainland coastline from the northern boundary of Spanish Sahara southwards to the southern boundary of South West Africa, the oceanic islands from the Salvage Islands southwards to Ascension, and all islands close to the African mainland coast are included in the area covered. Each species entry includes all traced records for the species, the names which have previously been applied to it in the area, and additional comments or evaluation, where necessary. Comments have also been made at generic level in some difficult case

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1969.tb01971.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

Because of the homothallic nature of many pteridophytes, two categories of mating are possible: intragametophytic selling (the origin of both gametes from a single gametophyte) and inter‐gametophytic mating (the origin of each gamete from a different gametophyte).Various morphological and genetical criteria (placement of the gametangia on the thallus, their sequence of ontogeny, the capacity for simple polyembryony and genetic self‐incompatibility) can be used to indicate the relative probability of intragametophytic selfing or intergametophytic mating. Only the former has genetic significance (i.e.complete homozygosity); if the latter is evidenced, then detailed studies of population variability are required to ascertain the breeding system.Three types of reproductive systems involve the gametophyte generation: intragametophytic selfing, intergametophytic mating and apogamy. Apogamy generally offers the shortest gametophyte generation and the least evolutionary potential, intergametophytic mating systems generally have the longest gametophyte generation and the greatest evolutionary potential, and intragametophytic mating systems are intermediate in both respectS. It is envisioned that the interaction between gametophyte ecology and evolutionary potential is important in the evolution of a taxon's reproductive sys

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1969.tb01972.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

Species ofBlechnum, Doodia, Woodwardia, LorinseriaandStenochlaenawere studied morphologically and genetically in an effort to obtain information relating to their reproductive biology.Woodwardia martineziiandStenochlaena palustriswere found to be apogamous.Lorinseria areolata, Blechnum unilateraleandB.nudumwere found to be adapted for intra‐gametophytic selling. Fifteen other sexual taxa were investigated and all were found to have adaptations making intergametophytic mating very likely. Thus of the 18 sexual taxa for which data are available, 8–33% have intergametophytic mating syst

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1969.tb01973.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY