摘要:

SUMMARYIn this third report of taxonomic studies on the freshwater species ofUlothrixKützing, the morphological and reproductive characteristics ofUlothrix implexa(Kützing) Kützing,U. tenuissimaKützing andU. zonata(Weber&Mohr) Kützing are discussed.U. implexais characterised by the lack of gametogenesis whereas the absence of asexual reproduction, occasionally occurring in culture, is accompanied by a very frequent appearance of branched rhizoid‐like outgrowths at irregular intervals in the filaments. The chloroplast morphology may show an affinity to the genusKlebsormidiumSilvia, Mattox&Blackwell.U. tenuissimashows both asexual and sexual reproduction. The occurrence of curled filaments containing gametangia and the occasionally pointed zoospores and gametes are characteristic for this species. In a certain growth stage of the chloroplast some morphological resemblance to the genusUrosporaAreschoug (HormisciaFries) is present.U. zonatashows an identical life cycle asU. tenuissima. It is proved that numerousUlothrixspecies which are described only are growth habits ofU. zonata.Both under long‐ and short‐day conditionsU. implexaonly shows reproduction by means of zoospores, whereas the other species, referred to in this paper, show asexual stages under a short‐day light regime, and gametogenesis under a long‐day photoperiod; sporophytes are observed to be fertile under short‐day conditions. The manner of occurrence of the species in nature agrees with the behaviour of the algae under different photope

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00971.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYOver 120 randomly selected strains belonging to 16 genera and to more than 80 species of Desmids were brought into uni‐algal culture and subjected to conditions provoking conjugation. Only 3 isolates – all homothallic – exhibited sexual reproduction:Closterium limneticumLemn.,Cl. moniliferumBory ex Ralfs, andMicrasterias papilliferaBréb. OfCl. limneticumno zygospores had previously been known. The, generally speaking, poor result of the experiment supports the theory that it is a lack of sexual potential rather than ecological factors which is responsible for the rare incidence of sexual reproduction in Desmids under natural cond

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00972.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYData are presented on distribution and ecology ofVaucheria compactain the Netherlands. A description is given of a sociation ofV. compacta, an estuarine community, often showing mass occurrence. From culture experiments in salinity ranges it is concluded that there are no “salinity races” but that a non‐modificative morphological variation is present in some antheridial characters. As a consequence of this, a new variety is described:Vaucheria compactavar.dulcis. At some occasions monoecious filaments were observed within this dioecious sp

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00973.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYThis paper deals with theVanguerieae, Cinchoneae, CondamineaeandRondeletieae, and concludes a study on the anatomy of the secundary xylem of theCinchonoideae+Ixoroideae. The taxonomically homogeneousVanguerieaeshow only little variation. Taxonomically theCinchoneae, Condamineae, andRondeletieae, placed near each other in theCinchonoideae, are rather heterogeneous. Their woods show also more anatomical differences, with a similar scala of variation within each tribe. Numerical analysis of the pattern of variation was undertaken. Cluster analysis showed a very distinct bipartition, which remained almost invaried while calculations were executed with different character weighings. This bipartition is not expressed in the existing taxonomic classifications. An attempt to distinguish the three tribes on the basis of their wood anatomy was made, but was unsuccessful.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00974.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYAs a sequel to biotaxonomic studies in Belgium, about 110 random population samples ofRumex acetosellaL. s.l. from a large part of France were studied. Representatives of this polyploid complex were of common occurrence everywhere except in areas with a subsoil rich in lime. Angiocarpy is wide‐spread, but gymnocarpy was only recorded from the French Alps. In contrast to the situation in Belgium, no correlation between the incidence of angiocarpy and a more fertile kind of soil could be established.Diploids (2n = 14) were found in the SE: Massif Central, Montagne Noire, Massif du Maure, and Massif du Mercantour in the Alpes Maritimes (altogether 36 populations); tetraploids (2n = 28, 23 populations recorded) are almost exclusively encountered in the Pyrenees and in the NE part of the Massif Central; and hexaploids (2n = 42, in 32 populations) appeared to be scattered over the remainder of the area studied, with a certain amount of sympatric overlap with the areas of the diploid and of the tetraploid chromosomal races in the Massif Central.In the zones of overlap an appreciable number of hybrids between 2n and 4n, and between 4n and 6n plants were encountered (in 11 populations).By far the large majority of the plants bear angiocarpous fruits irrespective of the level of ploidy, so that the alleged coupling between angiocarpy and diploidy (in the pertaining literature regarded as “R. angiocarpusMurb.”, with 2n = 14) must be rejected. In the Alpes Maritimes gymnocarpous diploids were found, which may be considered to represent a more primitive taxon among the aggregate.As far as can be ascertained, the distribution pattern of populations of theR. acetosellaaggregate is, generally speaking, characteristic of a complex species differentiated during and after the last Ice Ages. In the discussion attention is paid to the possible causes underlying the differences in the distributional patterns (such as vegetative reproduction at higher ploidy levels). In order to obtain a more complete picture of the complex the investigations are being pu

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00975.x

年代:1974

数据来源: WILEY

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00976.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe distribution ofS. jacobaeain The Netherlands is compared with local water‐table depth, degree of drainage and calcium content. As surface units, hour squares (5.25 km × 5.25 km) are used. Water‐table depth accounts for a greater part of the variance in the distribution of Ragwort than soil drainage. The variance accounted for by water‐table depth and calcium content is of the same order. In the category of soils which have a low water level and are calcareous at the same time, Ragwort is very frequent (in 96% of the squares).A significant relation of the distribution of the main consumer of Ragwort,T. jacobaeae, to soil drainage, as was found in England and Wales, could not be shown for The Netherlands. However, indications are given that egg distribution ofT. jacobaeaeis related to the area and density of Ragwort popul

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00977.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYA spontaneous mutant ofPetuniais described, which is characterised by the small size of its shoots, leaves and flowers. Apart from showing these size differences, the mutant has more rounded, suborbicular leaves with a wrinkled surface.In his transformation experiments withPetuniaHess obtained plants which according to his description agree in all details with this “dwarf” mutant, including the frequent occurrence of shoots with characters corresponding with those of the original plant form. He assumed that this particular type of plant had arisen as the result of a transplantation of a gene for leaf shape.However, our studies of the dwarf mutant revealed that the phenomena described by Hess can be explained as well by the incidence of somatic mutations and reversions in one of the two tunica layers of the shoot apex, rather than by the transplantation of gene material.The study of revertants of the dwarf mutant yielded data pointing to a predominant influence of the dermal layer on the morphogenesis of the whole pl

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00978.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYThis paper describes the CDC version of a formerly published computer program for the computation and graphical representation of pollen analytical data.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00979.x

年代:1974

数据来源: WILEY

摘要:

SUMMARYIn decapitatedAvenacoleoptiles the regeneration of the physiological tip is inhibited by glucose, galactose, lactose and raffinose. Galactose is the strongest inhibitor, and a further analysis of its action indicates that it inhibits auxin synthesis. The galactose effect is not antagonized by other sugars.Sucrose, maltose, fructose, rhamnose and ribulose have no influence on the regeneration.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1974.tb00980.x

年代:1974

数据来源: WILEY