摘要:

Some of the biological problems presented by bracken,Pteridium aquilinum(L.) Kuhn, are posed. Its taxonomic position within the Pteridophyta and the delimitation of entities within the genus are discussed on the basis of morphological and cytological evidence. The geographical ranges of the various brackens world‐wide are described and mapped in outline, and emphasis placed on reviewing the natural ecological role of bracken in plant communities throughout the world. Further geographic areas where taxonomic investigation ofPteridiumis most needed are indicated, and evidence of the reproductive, dispersal, establishment, colonizing ability and vegetative persistence of bracken is reviewed. Its palaeobiological spread, with associated vegetational history, and the effects on this of anthropogenic influences—better known than are comparable details for any other pteridophyte—are detailed, and the present magnitude of the resulting bracken problem in Britain (and especially in upland Britain) indi

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02010.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Variations in flavonoids extracted from fronds suggest thatPteridium aquilinum(L.) Kuhn is a monospecific genus. A wide range of secondary plant substances also occur in bracken including sesquiterpenoids, echydones, cyanogenic glycosides, tannins and phenolic acids.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02011.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The principal events in spermatogenesis, in particular those occurring in the final stage in which the isodiametric spermatocyte is transformed into the helical spermatozoid, are described. The origin of the blepharoplast remains obscure, but its subsequent development is now well known. Firm information is still lacking concerning the manner of growth of the microtubular ribbon and flagella, and the nature of the forces shaping the nucleus. The spermatozoid ofPteridiumhas much in common with those of other archegoniates, and there are significant parallels with the motile cells of chaetophoralean algae.Oogenesis involves extensive cytochemical changes, as well as ultrastructural ones, extending over three cell generations. The mature egg contains relatively large amounts of cytoplasmic deoxyribo‐ and ribo‐nucleic acids, part of the latter informational in nature. Considerable autophagy, including partial elimination of cytoplasmic organelles, occurs early in oogenesis. Termination of this stage is marked by the secretion of an acetolysis‐resistant membrane around the maturing egg, completing its isolation from the gametophyte. Maturation also involves nucleolar activity, bodies of nucleolar origin entering nuclear evaginations. Most evaginations are sac‐like; others, formed by an overarching sheet of nucleus, hood‐like. The fate of the evaginations is problematical. Some may become free and differentiate into mitochondria or plastids. The contents of the egg nucleus remain less dense than the cytoplasm and the chromatin highly dispersed.Only very few eggs are viable at fertilization. The manner of syngamy is not yet clear. Immersion of the male gamete in the female cytoplasm causes freeing of the nucleus from the microtubular ribbon, and reconstitution of its envelope. It now falls into irregular loops within the funnel formed by the coiled ribbon. Orientation of this funnel such that the anterior end of the male nucleus contacts the female is probably essential for karyogamy. Following the formation of an orifice, the male chromatin moves into the female nucleus. The male nuclear envelope is probably resorbed, and the other parts of the spermatozoid eventually digested. The special egg membrane becomes incorporated into the common wall between the gametophyte and zygote, and may prevent the transference of complex

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02012.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The role of sugar nucleotides in polysaccharide synthesis is discussed. The presence of acid soluble nucleotides in bracken rhizomes was demonstrated (20 μmol/kg fresh weight) and the uridine series was shown to predominate accounting for some 80% of the total. The following were identified, UDP‐glucose (60%), UDP‐galactose (15%), UDP‐xylose (9%), UDP‐arabinose (3%), UDP‐glucuronic acid (4%), GDP‐mannose (6%) and GDP‐fucose (3%). It is probable that these sugar nucleotides supply the full complement of sugars identified in the carbohydrate fracti

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02013.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The amounts of dry matter, mobile carbohydrate and reserve carbohydrate have been determined in bracken fronds and buds, frond‐bearing rhizomes and storage rhizomes over a period of 13 months. Dry matter and reserve carbohydrate levels are closely linked, especially in the rhizomes, falling from May to the beginning of July and rising until complete frond death at the end of September; but variations occur between frond‐bearing and storage rhizomes. The carbohydrate reserve of frond‐bearing rhizome is rapidly exhausted by the developing fronds and further carbohydrate is drawn from the storage rhizomes, but a concurrent fall in mobile carbohydrate suggests that the rate of conversion of reserve carbohydrate is slower than the rate of translocation to the fronds. By August, there is an accumulation of carbohydrate in the frond‐bearing rhizome, which is followed by a fall in September and this again suggests low enzyme activity in the storage rhizome, but also that sink strengths in bracken are in the order (1) developing buds, (2) storage rhizome, (3) frond‐bearing rhizome.The responses of bracken to cutting and herbicide‐application are discussed in relation to sink strengths and a low level of enzyme activity in the stor

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02014.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Bracken is a weed that strongly dominates a wide variety of vegetation types throughout the world. The primary mechanism of interference that this fern brings to bear upon associated plants that allows it to establish and maintain dominance is allelopathy. But due to the nature of the interaction between allelopathy and the environment, bracken has evolved a mechanism of toxin release which allows the fern to exert its dominance most effectively in each particular habitat in which it grows. In southern California, toxin release is timed for the initiation of the wet season and thus the initiation of germination of associated plants. Toxins come primarily from the dead, standing fronds. In the Pacific Northwest, toxin release is timed for the breaking of dormancy in spring after the snow melts and soil temperature rises. Toxins come primarily from bracken litter, roots and rhizomes. In tropical Costa Rica, toxin release takes place all year round, timed for the continual growth of associated plants. Toxins come primarily from a continual production by the green fronds. The interrelationship between allelopathy and the environmental complex is discussed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02015.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The production of tumours in animals by the carcinogenic action of bracken fern (Pteridium aquilinum(L.) Kuhn) is described. One of the substances responsible has been identified as shikimic acid, and evidence is presented that it is a powerful mutagen. The isolation of another toxin which gives rise to malignancies is nearing completion. The possibility of an environmental human hazard is considered.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02016.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The toxicity of bracken (Pteridium aquilinum(L.) Kuhn) to animals is complicated because this plant elaborates more than one type of agent harmful to livestock. An enzyme, thiaminase I, which destroys thiamine, is responsible for the neurotoxic syndrome. Using a radiochemical assay, the distribution of thiaminase I activity in bracken throughout the growing season has been ascertained: levels are high in the rhizome and young buds, but fall sharply in the fronds as the aerial parts of the plant unfold.The so‐called thermostable ‘antithiamine’ factors present in bracken and other plant species are discussed.The biochemical lesions of thiamine deficiency in animals are briefly outlined, and the clinical syndrome caused by the inclusion of bracken fronds or rhizomes in the diet for simple‐stomached animals (rat, horse, pig) and a ruminant (sheep) are described.All these neurotoxic syndromes respond to thiamine therapy in a dramatic way, if administered during the early stages of the

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02017.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Investigations on the decomposition of bracken petioles, over a five‐year period on six adjacent soil types, including moder‐type humus, mull and peat, are reviewed. Changes in gross physical features, chemical composition, pH and dry weight are outlined. The succession of colonizing fungi is described and related tofungal activities.Until the petioles were buried in the litter layer, decomposition occurred at different rates on the various sites, the rate on moder>mull>peat, but the sequence of events was similar. Large proportions of readily leached components were removed in the first few months, but 95% loss of dry matter was estimated to occur only after 11–23 years. The majority of fungi were species cosmopolitan on litter, the population becoming less specialized as decay advanced. The succession resembled those on some other woody tissues, lignin and cellulose decomposers predominating before sugar fungi. From field observations and laboratory experiments, the Basidiomycete Mycena galopus (Pers. ex Fr.) Kummer appeared to be the most active of the fungal decomposers.Some ecological and economic implications of the decomposition of bracken litter are briefly discussed, including its effect on soil type, and advantages of bracken compared with straw as bedding for farm an

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02018.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Laboratory experiments on fungal pathogens of the gametophyte generation are described and the possible causative agents associated with disease of bracken colonies in the field discussed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb02019.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY