摘要:

The thallus ofPenicillusis composed of two filament types: axial filaments of indeterminate growth and laterals of determinate growth. In vegetative reproduction new plants arise from horizontal rhizoids. Four stages can be distinguished in development. In theprimordiumstage the tip of a rhizoid swells and forms a primordium. In thegermlingstage ascending and descending axial filaments arise from the primordium, the former grow into a fascicle and give rise to lateral saccate branches, each of which forms an ascending and a descending arm and branches further into rhizoid‐like branchlets. Together these structures constitute the foundation of the stipe. At the same time the descending axial filaments elongate and become main rhizoidal filaments with lateral rhizoidal branchlets. In theearly juvenilestage the stipe is formed. The elongating ascending axial filaments form a medulla while their laterals produce a cortex. In thelate juvenilestage the axial filaments form the capitulum.TheEsperastate ofPenicilluslacks a stipe since the ascending axial filaments do not join in a fascicle.Esperahas been grown in laboratory cultures fromPenicillusplants collected in the Caribbean region and also been found uncommonly in nature in this area. This state may be a response to environmental stress.The flattening of thalli and their orientation perpendicular to the direction of waves are discussed.A comparison ofPenicillusandCodiumindicates that at least two types of development exist in multiaxial Eusiphoniida

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1977.tb01176.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Equisetumgametophytes possess extensive powers of regeneration without showing any signs of diminished vigour or abnormal development. Isolated lamellae, pieces of antheridial and archegonial branches were used to analyse gametophyte morphogenesis and sex determination. Intact individuals and subcultured sexual branches never revert to a vegetative state. Transplantation of apical pieces of archegonial branches on to fresh medium delays the onset of antheridium formation indicating phenotypic control. On the other hand, male branches invariably continue producing antheridia. Experimentally induced adventitious branches on lamellae are interpreted as the result of physiological isolation from inhibitors. In intact individuals these adventitious branches are always antheridial: after subculturing, archegonial branches are also produced, demonstrating that the gametophytes ofEquisetumare all potentially bisexual. Isolated lamellae regenerate secondary gametophytes, the sexual ratios between which vary between species, but lamellae from archegonial tissues invariably produce more female individuals, probably reflecting the different sizes of the respective lamellae. The view that mixtures of intact male and bisexualEquisetumgametophytes result from inherent physiological differences between the spores is not supported.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1977.tb01177.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Gametophytes ofAsplenium pimpinellifoliumFee andLygodium heterodoxumKze., occurring as natural populations in Veracruz, Mexico, were studied with respect to their spacing, size, and number of antheridia and archegonia. Small gametophytes, 0.3‐2.2 mm in width and growing in colonies, usually had high numbers of antheridia. Gametophytes of the same size, growing at least 1 5 cm from the nearest neighbour, had few antheridia. In the colonial gametophytes there was a strong correlation between heavily antheridiate ones and their proximity to large archegoniate gametophytes. The data are the first to suggest the presence of an antheridogen system operating in nature, with concomitant opportunities for cross‐fertilization. The rôle of polyploidy in storing genetic variation and the rôle of antheridogen‐mediated out‐crossing in releasing variation are seen as co‐adaptive phenomena i

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1977.tb01178.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

From studies in the field, botanic garden and herbarium we concluded that the following four species ofDryopterisgrow on the Canary Islands:D. aemula (n= 41) so far found only on Gomera;D. pseudomas (n= 82, apogamous) similarly recorded only for Gomera;D. oligodonta (n= 41) the most common representative of the genus in the Islands is possibly an old Canary endemic related to some African species;D. guanchicaa new tetraploid species (n= 82) hitherto confused withD. austriaca (D. dilatata).On four islands of the Azores the following were found:D. aemula (n= 41);D. azorica (n= 41);D. pseudomas (n= 82, apogamous); andD. crispifoliaa new tetraploid species (n= 82) which is very distinct when living but in the dried pressed state is difficult to differentiate fromD. austriacaandD. guanchica.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1977.tb01179.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The results of two expeditions to Central Africa to collect and study cycads, mainlyEncephalartosspecies, are presented. Further morphological information on the living plants growing in their natural habitats is given, together with new localities. Species delimitation is reassessed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1977.tb01180.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY