The cytology of Halidrys siliquosa (L) Lyngb

Resting nuclei in vegetative apices and developing receptaclesof Halidrys siliquosa (L) Lyngb. contain several large, Feulgen-positivegranules. The number of granules varies from two to nine inboth vegetative cells and developing gametangia. Approximately55 chromosomes have been counted in the meristoderm cells ofthe apical groove, and approximately 30 in the first, second,and third divisions of the antheridial initials.     

The Structure and Development of Himanthalia lorea (L.) Lyngb1

The development of H. lorea has been followed in detail andcomparisons made between comparable stages of development ofplante from exposed and from sheltered habitats. The origin and course of the longitudinal hyphae ie traced,and it is found that the distance behind the apex at which theyarise varies at different stages of development. The very pronounced surface growth leads to extreme elongationof the medullary cells which also develop characteristic dilationsat the horizontal septa. In the receptacles the production of the horizontally runninghyphae appears to be connected with the formation of centralair-spaces. In the older receptacles the cells of these hyphaebecome extremely swollen and form irregular blocks of pseudo-parenchymatoustissue. The production of longitudinal hyphae is more marked in plantsfrom more exposed habitats, and the inner cortex has thickerwalled cells where the plants have to endure longer periodsof intertidal exposure.     

Observations on the biology of Glossiphonia heteroclita (L.)

Summary A population of Glossiphonia heteroclita (Linnaeus) was studied in a pond situated in the grounds of the University College of North Wales, Bangor, Caernarvonshire, from November 1965 to September 1966.Monthly samples were obtained by placing roofing slates in the pond and collecting the leeches which settled on their undersides. These leeches were weighed, and examined for the presence of food in their gut. This provided the data for the construction of histograms of weight frequency, from which their life-history could be inferred.During the summer, breeding leeches were kept in the laboratory, at an average temperature of 14°C. Experiments were carried out to investigate the relationship of the young leeches with their parent, and the feeding behaviour of G. heteroclita.The evidence suggests that G. heteroclita is an annual. A proportion of the leeches which had over-wintered, began to reach maturity in April and breeding commenced in May. By September most of these had produced offspring and many of the heavier leeches had died.About twenty-five eggs were laid into a thin-walled cocoon, which was held under the posterior end of the body. After three or four days the eggs became arranged in a single layer, and were firmly attached to the parent by means of the embryonic attachment organ. The embryos hatched sixteen days later, at 14°C, and then attached to the parent by their posterior suckers. The young leeches remained attached to the parent for at least ten days, by which time their store of yolk was used up. Young leeches separated from their parent soon after hatching died.Although young leeches which were placed in a separate dish from their parents several days after hatching, survived well, they were not able to take advantage of certain types of food.Young leeches separated from their parents, but kept in the same dish usually re-attached in a few hours. They also readily attached themselves to other adult G. heteroclita, but not to other species in the same family e.g. Glossiphonia complanata and Helobdella stagnalis.In the field, leeches which hatched early in the summer, weighed up to 8 mg in September. Those which hatched later did not grow so rapidly. Many small leeches were found in the population throughout the winter. The data on feeding showed that it occurred infrequently during the winter. There was considerable mortality in April, just before the onset of breeding.The behaviour experiments, supported by immunological evidence, suggested that the main food of G. heteroclita in the College Pond, was Lymnaea stagnalis. The leeches did not accept undamaged snails. They also fed on damaged Enchytraeus albidus.

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Zusammenfassung Von November 1965 bis September 1966 wurde in einem Teich im Gelände des University College of North Wales, Bangor, Caernarvonshire, eine Population von Glossiphonia heteroclita (Linnaeus) wissenschaftlichen Untersuchungen unterzogen.An der Unterseite von Dachschiefern, die in den Teich gestellt wurden, siedelten sich Egel an. Jeden Monat wurden these Egel, die einen Ausschnitt der ganzen Population im Teich darstellten, gesammelt. Diese Egel wurden gewogen und der Darm auf das Vorhandensein von Nahrung geprüft. Die Untersuchungen ergaben Daten zur Aufstellung von Histogrammen der Gewichtsfrequenz, von denen der Lebenszyklus konstruiert werden konnte.Im Sommer wurden Egel während der Vermehrung im Laboratorium bei einer Durchschnittstemperatur von 14°C gehalten. Die Beziehungen von jungen Egeln zum Muttertier und die Art und Weise der Nahrungsaufnahme von G. heteroclita wurden experimentell untersucht.Die Beobachtungen weisen darauf hin, daß G. heteroclita eine einjährige Lebensdauer hat. Ein Teil der Egel, die überwintert hatten, begannen im April ihre Geschlechtsreife zu erreichen und sich im Mai zu vermehren. Bis September hatten die meisten dieser Egel Junge produziert, und viele der schwereren Egel waren eingegangen.Etwa 25 Eier wurden in einen dünnwandigen Kokon gelegt, der sich unter dem hinteren Ende des Körpers befand. Nach 3 bis 4 Tagen batten sich die Eier einschichtig gruppiert und waren mit Hilfe der embryonischen Haftorgane fest an dem Muttertier befestigt. Bei 14°C schlüpften- die Jungen nach 16 Tagen aus und befestigten sich mit ihren hinteren Saugnäpfen an das Muttertier. Nach Verbrauch des Dottervorrats blieben die jungen Egel nach mehrere Tage an dem Muttertier festgesaugt. Die Jungen, die kurz nach dem Ausschlüpfen vom Muttertier getrennt wurden, gingen ein.Obwohl junge Egel, die mehrere Tage nach dem Ausschlüpfen vom Muttertier getrennt und in einem anderen Behalter untergebracht wurden, gut überlebten, waren sie jedoch nicht fähig, gewisse Arten von Nahrung aufzunehmen.Junge Egel, die vom Muttertier getrennt wurden, jedoch in demselben Behälter blieben, saugten sich gewöhnlich nach wenigen Stunden wieder fest. Sie saugten sich ohne weiteres nicht nur bei dem Muttertier sondern auch bei anderen erwachsenen G. heteroclita wieder fest, nicht aber bei anderen Arten der gleichen Familie, z.B. Glossiphonia complanata und Helobdella stagnalis.Freilebende Egel, die am Anfang des Sommers ausschlüpften, wogen im September bis zu 8 mg. Diejenigen, die später ausschlüpften, wuchsen nicht so schnell. Während des ganzen Winters wurden viele kleine Egel in der Population gefunden. Die Daten der Ernährungsfrequenz zeigen, daß während des Winters Nahrung nicht häufig aufgenommen wurde. Kurz vor Beginn der Vermehrung im April war die Sterblichkeit beträchtlich.Die Verhaltensexperimente, gestützt auf immunologische Nachweise, deuten darauf hin, daß die Hauptnahrung von G. heteroclita im College-Teich Lymnaea stagnalis war. Die Egel nahmen unbeschädigte Schnecken nicht an. Sie frassen auch verletzte Enchytaeus albidus.

     

Cytology of oocytes in ground squirrels (Citellus citellus L.)

Oocytes of primordial, primary, growing, and Graaf follicles of the ovaries of 96 ground squirrels (Citellus citellus L.) were studied during the four seasons of the year. Multilamellar bodies in the oocytes were observed by electron microscopy. The bodies underwent changes during the follicle growth. The vesicles included in the multilamellar bodies were filled with an amorphous substance, while in Graaf follicles trapezoidal, rhomboidal, and hexagonal inclusions were found. The primordial follicle of the oocyte had no Balbiani body. In the hibernating ground squirrel the functions of the Balbiani body were probably performed by the multilamellar bodies, which were considered to be analogous to the Balbiani body.     

Observations on the ultrastructure of the carp liver (Cyprinus carpio L.)

The paper presents information about the fine structure of the sinusoids, the space of Dissé, the development of the bile canaliculi and some compartments of the hepatocytes in the liver of the carp. The sinusoids are covered completely by flat endothel cells. The plasma of these cells contains numerous vesicles. The endothelial cells possess plasmatic processes, which extend into the space of Dissé. The fine structure of the space of Dissé corresponds to that of mammals, the existence of fibrebundles included. The bile canaliculi don't develop intracellularly as described by other authors. They run intercellularly as in mammals, but they form diverticles which reach into the plasma sideways. The rough ER was found in two types. Outwardly the liver is limited by a layer of connective tissue existing in two different layers.     

Observations on the growth,fruiting and longevity of Furcellaria fastigiata (L.) Lam.

Summary Measurements made upon plants of Furcellaria fastigiata (L.) Lam. grown in situ in a lower littoral logoon community at Aberystwyth show that this species is a slow growing perennial. Maximum growth rate occurs early in the year between March and May. Annual increase in length is about 3.4 cms. and the plants reach maturity in about 4 to 6 years in this particular habitat. Growth rate, maximum size and longevity depend to a considerable extent upon environmental factors, particularly upon light and exposure to wave action.

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Zusammenfassung Die Messungen, die an Pflanzen der Art Furcellaria fastigiata (L.) Lam. vorgenommen wurden, die in einer nur bei absolutem Tiefstand der Ebbe völlig abgeschlossenen Lagunengemeinschaft bei Aberystwyth in situ gewachsen waren, zeigen, dass diese Spezies zu den langsam wachsenden Perennierenden gehört. Der Maximale Wachstumsbetrag kommt im Frühjahr zwischen März und Mai vor. Das jährliche Längenwachstum betragt 3,4 cm. Die Reife der Planze in dieser speziellen Gemeinschaft tritt nach ungefähr 4–6 Jahren ein. Der Wachstumsbetrag, die Maximale Grösse und die Lebensdauer hängen in beträchtlichem Masse von Umweltsfaktoren ab, besonders vom Licht und davon, ob der Standort der Einwirkung der Wellen ausgesetzt ist.

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Marine Biology Station, Menai Bridge

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The observational work reported in this paper was carried out at the Department of Botany, Aberystwyth.     

Observations on the biology of Subcoccinella vigintiquattuor-punctata (L.) in southern England

• 1 Subcoccinella 24-punctata (L.) is exclusively phytophagous, and is widely distributed throughout Britain.
• 2 Under laboratory conditions the duration of pre-adult instars is about 6 weeks. Adults appear from the end of June onwards. Many enter reproductive diapause at the end of July, but remain active till the end of October.
• 3 Reproductive diapause is determined by the interaction of photoperiod and temperature.
• 4 Hibernation is unstable, and there may be high mortality in overwintering adults. These finally die during May and June.
• 5 The cool temperate climate limits the population size, preventing it from reaching pest proportions.

     

Cytology of two species of winged bean, Psophocarpus tetragonolobus (L.) DC. and P. scandens (Endl.) Verde. (Leguminosae)

Karyotype morphology of Psophocarpus tetragonolobus and P. scandens is described and the behaviour of chromosomes at meiosis discussed. Both species have a chromosome number of 2n = 18 and similar karyotypes of a sort unusual within the Phaseolinae. Differences between the species in detailed morphology of the chromosomes agree with data from external morphology, palynology and crossability in indicating that P. scandens cannot be the immediate wild ancestor of domesticated P. tetragonolobus . Study of meiotic chromosomes and analysis of qualitative and quantitative variation in Papua New Guinean P. tetragonolobus suggest that there are few restrictions to recombination other than those imposed by predominant self-pollination, The bearing of these data on the taxonomic relationships of Psophocarpus and on chromosomal evolution within the Phaseolinae is discussed.     

Cytology of egg maturation in the silkworm (Bombyx mori L.) in artificial parthenogenesis

The orientation of bivalentss in the first meiotic metaphase was studied on the squash preparations and sections of eggs in Bombyx mori L., Antheraea pernyi Guèr and Carpocapsa pomonella L. The reduction fissure of bivalents separating the homologous chromosomes lies in the plane of spindle equator; the equation fissure separating the sister chromatids is parallel to the long spindle axis. Complicated rearrangements are observed in the nuclei of the silkworm eggs stimulated to ameiotic parthenogenesis by the high temperature dissociation of bivalents, full destruction of spindle, formation of a new spindle and metaphase plate. The latter includes univalent chromosomes involved in the equation division. As a result, two genetically identical pronuclei with the somatic set of chromosomes are formed.     

Observations on some epibionts of gulf-weed,Sargassum natans (L.) Meyen

The succession of epibionts on gulf-weed, Sargassum natans (L.) Meyen, is described. Only the hydroid Clytia noliformis (McCrady) colonizes the newest algal growth, spreading rapidly from below towards the frond tips by means of stolons. The remaining species — the bryozoon Membranipora tuberculata (Bosc), the spirorbid Janua formosa (Bush) and the blue-green alga Calothrix crustacea Schousb. & Thurs. — establish themselves through a free-swimming phase but, instead of attaching near the meristem as is usual on other algae, the larvae and hormogonia (dispersal phase of Calothrix) settle well away from the growing tip of the Sargassum. Such behaviour is consistent with the view that tannins present in the young thallus inhibit the establishment of the surface microflora which is a pre-requisite for the settlement of larger epibionts.Janua shows a strong preference for the bladders of the Sargassum, and Calothrix for the leaflets; but Membranipora appears to settle equally well on bladders, leaflets, and stem.Observations on young colonies of Membranipora reveal that the metamorphosing larvae were orientated with respect to the axis of the Sargassum leaflets. Water flow, which has previously been considered as likely to provide a directional stimulus for such orientation, cannot be the operative factor in this case.     

Observations on the fine structure of the endophyte of the root nodules of alnus glutinosa (L.) gaertn.

Summary Electron micrographs have been prepared showing different stages in the development of the endophyte in Alnus glutinosa root nodules. Although the complete life cycle of the organism has not yet been worked out it is concluded that it is an Actinomycete. The organism can exist as a septate, branching filament of diameter 0.7–1.0 . However, under certain conditions within the nodule, the endophyte can form spherical sub-divided vesicles 4–5 in diameter and it is suggested that these vesicles are analogous to sporangia. Yet again under other conditions the organism fragments to form bacteroids. It would appear that the different forms of the organism are associated with different seasons of the year and with different metabolic patterns, of particular interest in this connection is the fixation of nitrogen which is associated with the nodule symbiosis.     

Biomass dynamics of exotic Sargassum muticum and native Halidrys siliquosa in Limfjorden,Denmark—Implications of species replacements on turnover rates

The expansion of Sargassum muticum in the Danish estuary Limfjorden between 1984 and 1997 was followed by a decrease in abundance of native perennial macroalgae such as Halidrys siliquosa. Although commonly associated with the expansion of exotic species, it is unknown whether such structural changes affect ecosystem properties such as the production and turnover of organic matter and associated nutrients. We hypothesized that S. muticum possesses ‘ephemeral’ traits relative to the species it has replaced, potentially leading to faster and more variable turnover of organic matter. The biomass dynamics of S. muticum and H. siliquosa was therefore compared in order to assess the potential effects of the expansion of Sargassum. The biomass of Sargassum was highly variable among seasons while that of Halidrys remained almost constant over the year. Sargassum grew faster than Halidrys and other perennial algae and the annual productivity was therefore high (P/B = 12 year⁻¹) and exceeded that of Halidrys (P/B = 5 year⁻¹) and most probably also that of other perennial algae in the system. The major grazer on macroalgae in Limfjorden, the sea urchin Psammechinus miliaris, preferred Sargassum to Halidrys, but estimated losses due to grazing were negligible for both species and most of the production may therefore enter the detritus pool. Detritus from Sargassum decomposed faster and more completely than detritus from Halidrys and other slow-growing perennial macrophytes. High productivity and fast decomposition suggest that the increasing dominance of S. muticum have increased turnover of organic matter and associated nutrients in Limfjorden and we suggest that the ecological effects of the invasion to some extent resemble those imposed by increasing dominance of ephemeral algae following eutrophication.     

Further Observations on Root--Shoot Equilibria in Perennial Ryegrass (Lolium perenne L.)

Plants of Lolium perenne L. (cv. S. 23) were grown in a heatedglasshouse. Two experiments were performed, both during earlysummer. One used a sand/solution rooting medium and includedlow-nitrogen (0.17 parts per 10⁶) and shade (20.2 per cent illumination)treatments; the other used aerated solution culture and involvedtwo levels of shading (20.2 and 6.1 per cent illumination),in addition to controls. In both experiments growth and ratesof potassium, magnesium and calcium uptake were studied throughthe calculation of various growth-functions from fitted curves. Despite the effects of treatment and environment, a constantinverse relationship was found between the mass ratio of rootsand shoots and their activity ratio. These new results wereadded to some previously published to form a combined model:mass ratio = 0.051 + 45.7 (1/activity ratio) where activityratio is expressed as specific absorption rate for potassium(in µg K mg root^–1 day^–1)/unit shoot rate(rate of increase of whole-plant dry weight per unit shoot weight,mg mg^–1 day^–1). The implications of this relationshipare discussed and a further model is put forward in which rootactivity is expressed in terms of the uptake of the sum of thepotassium, magnesium and calcium contents of the plant.