摘要:

SUMMARYSome observations on the cytokinetic and mitotic mechanism in the filamentous green algaeUlothrix zonata(Weber&Mohr) Kützing andU. tenuissimaKützing are presented. The general pattern of division appears to be similar in both species, and includes a precocious cleavage furrow formed at late interphase. Cross wall formation is not completed until telophase. By late prophase the centriole pair has duplicated, and each daughter pair migrates to a position distinctly lateral to the spindle poles. As soon as the daughter nuclei have separated, formation of the new septum is completed by coalescence of presumably Golgi derived vesicles in the plane of the pre‐mitotically developed cleavage invagination, so there is no ingrowth of the furrow itself. A phycoplast as typically found in certain other filamentous green algae (e.g.,Stigeoclonium) is not formed. A comparable division mechanism has been reported previously in four cases, i.e., inUlva, Pseudendoclonium, Trichosarcina, and in an alga of uncertain identity (UTEX strain LB 653). It is concluded that these taxa are related organisms, and can be referred to as UlvophyceaesensuStewart&Mattox. The taxonomic status of a number of doubtful species ofUlothrixis discussed in the light of both light microscopical and electron microscopical evide

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01711.x

年代:1983

数据来源: WILEY

摘要:

SUMMARYCaulerpa bilobais described as a new species. It is characterized by having two‐lobed ramuli, a formerly unknown feature in this genus. The relation withC. vickersiaeBørgesen andC. ambiguaOkamura is discuss

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01712.x

年代:1983

数据来源: WILEY

摘要:

SUMMARYIn three experiments the effects of light intensity and nutrient supply (nitrate or phosphate) and their combined effects on the growth and morphogenesis of two shade‐tolerant plant species and a non‐tolerant species were studied. Nutrient supply was limited by placing the plants on a standard nutrient solution for a limited period each day and placing them on a nitrogen‐free or phosphate‐free solution for the rest of the day. The effects of light intensity and nitrate supply on growth and morphogenesis showed a marked interaction: low nitrate supply caused a much greater decrease in the relative growth rate under high light intensity, because of much larger changes in the dry matter ditribution; the net assimilation rate was only slightly affected by nitrate supply. The effects of light intensity and phosphate supply on the dry matter distribution and the net assimilation rate both showed interaction, but the effects on the relative growth rate were independent. Low phosphate supply caused greater changes in the dry matter distribution under high light intensity and a greater decrease in the net assimilation rate under low light intensity; the relative growth rate decreased to the same extent under both high and low light intensities. The experimental data were compared with the balanced quantitative model for root/shoot ratios proposed by Thornley(1972). The results were very satisfactory, but it was concluded that the model must be used in its exact form and that the use of approximations cannot be

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01713.x

年代:1983

数据来源: WILEY

摘要:

SUMMARYIn France and The Netherlands inMetasequoia glyptostroboides(Hu and Cheng) only purely female cones are present budding at the end of February. In the absence of any male gametophytic tissue a normal and complete female gametophyte develops. The developments from free nuclear gametophytes to the mature egg cells are presented at light and electron microscopy level. The functional influence of the male gametophyte as a prerequisite for female gametophyte development is questioned and discussed for the different developmental stages as observed inMetasequoiaand for other Gymnosperms. In case ofMetasequoia, it is suggested that the female gametophyte is basically autonomous.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01714.x

年代:1983

数据来源: WILEY

摘要:

SUMMARYIt has been observed that under control conditions, the abscission of flowers inPhaseolus vulgarisproceeds via the breakdown of both the middle lamella and the primary wall of the cells in the abscission layer of the pedicel. However, under conditions of water stress, the dissolution of the middle lamella occurs much faster than the breakdown of the primary wall. The difference in the integrity of the cell wall of the abscising cells under these two conditions is discussed in relation to differential enzyme activation of the separation process.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01715.x

年代:1983

数据来源: WILEY

摘要:

SUMMARYA late medieval clearing ofAlnusforest at the edge of the Dinkel valley and at the foot of the Ootmarsum hill (Twente, Eastern Netherlands) is revealed from pollen analysis of peat developed near a source of a vanished brooklet. The clearing later developed from a wet sedge‐meadow to a pasture. Details on the medieval forest history are also discusse

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01716.x

年代:1983

数据来源: WILEY

摘要:

SUMMARYTwo species ofPetunia, P. linearisandP. calycinawere grown from seed collected in the wild. Their chromosome number (2n = 18) and karotype morphology have been studied. Both species seem to be related toP. parviflora, which found support in peroxidase isozyme data. The three 2n = 18 species differ considerably from thePetuniaspecies with 2n = 14 chromosomes.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01717.x

年代:1983

数据来源: WILEY

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01718.x

年代:1983

数据来源: WILEY

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01719.x

年代:1983

数据来源: WILEY

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1983.tb01720.x

年代:1983

数据来源: WILEY