L'effetto Di Popolazione Nelle Colture Del Polline: Alcuni Aspetti Della Sua Natura

Abstract

Pollen population effect in artificial culture: some aspect of its nature. — The ability of pollen to grow on several rather different artificial media has not yet allowed investigators to determine the best conditions for each species. However a common requirement for all kinds of pollen is a high density of pollen grains on the culture medium, that stimulates the pollen germination and the pollen tube growth. Many investigators dealing with the causes of that phenomenon failed to reach a convincing conclusion on its causes. Our experiment was set to test the ability of an unknown pollen growth factor (PGF) to diffuse from growing pollen into the medium. Consequently after removal of the pollen culture a second pollen population grown on the same medium should be able to use the PGF eventually dissolved in it. Widely scattered populations of Malus pollen were grown onto membrane filters in contact with such «preconditioned» media and tested for their ability to germinate. Because the percentage of germination were lower than expected, wide-pored membranes (8.0 μ instead of 0.8 μ) were tested, thus achieving a rate of germination as high as that of the crowded populations of pollen. Hence it was argued that the PGF is water soluble, but is absorded on the membrane before reaching the contact of the pollen. However if the pores surface is small enough to be saturated by part of the PGF the free remainder is still enough to stimulate the small population of pollen. To test the assumption (BREWBAKER and KWACK, 1963) that simply Ca++ supported by other cations is the PGF, Ca++, Mg++ and K+ have been supplemented to the Standard medium as sulfates at a 10—⁴ M concentration, combined in a factorial design. The results are reported in table 2 and can be briefly summarized as follow. The most efficient ion appears to be K+, followed by Ca++ and Mg++. Each one is able to increase significantly the rate of germination with respect to the following ion, but two negative interactions (Ca × K and Mg × K, P: 0.01) were found to be significant. Because the only significant interactions were with K+, and because the mixtures containing K+ significantly differ but from treatment with Ca++ and Mg++, and not from K+, it could be tentatively stated that the negative interaction is at expenses of the K+ stimulatory effect (see fig. 1). The joint evaluation of both experiments strongly suggests the idea that the PGF is an organic rather than an inorganic molecule, with high affinity with the membrane on which it can be adsorbed. Most probably this organic growth factor needs an inorganic ion to display its stimulatory effect, but this cannot be identified with the PGF. In fact none of the tested inorganic molecules is adsorbed on the narrow pored membrane and they display full stimulatory activity through it. The second experiment seems to suggest the idea that such inorganic ion is K+.     

Late Pleistocene and Holocene pollen stratigraphy at Lago di Vico, central Italy

A new pollen record from Lago di Vico (core V1) provides fundamental new information towards reconstruction of flora and vegetation history in central Italy during the last 90 000 years. The chronological framework is secured by seventeen AMS¹⁴C dates, one⁴⁰Ar/³⁹Ar date and tephra analyses. At the base of the pollen record, i.e. shortly after the⁴⁰Ar/³⁹Ar date 87 000±7000 B.P., three phases with significant expansion of trees are recorded in close succession. These forest phases, which stratigraphically correspond to St Germain II (and Ognon?) and precede pleniglacial steppe vegetation, are designated by the local names Etruria I, Etruria II and Etruria III. During the pleniglacial, a number of fluctuations of angiosperm mesophilous trees suggest the presence of tree refugia in the area. The lowest pollen concentration values are recorded at ca. 22 000 B.P. which corresponds with other pollen records from the region. The late-glacial is characterized by an expansion in the arboreal pollen curves that is less pronounced, however, than in other pollen profiles from Italy. The Holocene part of the profile is consistently dominated by deciduous oak pollen. No major changes in arboreal pollen composition are recorded but several marked and sudden declines of the tree pollen concentration suggest that the forest cover underwent dramatic changes. Clear evidence for human impact is recorded only when cultivated crops became important which dates to ca. 2630±95 B.P.     

Aspetti Della Biocenosi Coralligena in Due Stazioni Dei Bacini Occidentale Ed Orientale Del Mediterraneo

Abstract

Facies of the coralligenous biocoenose in two stations of the Western and Eastern Mediterranean Basins. — The benthic comunities of circalittoral region have been studied by diving technique in the Western and Eastern Mediterranean Basins. The facies of the coralligenous biocoenose which show a larger difference between the two Basins are: 1) the communities of non calcareous algae in biotopes with constant direction depth streams and 2) the precoralligenous facies. These communities in the Aegean Sea are characterized by Sargassum linifolium, Cystoseira corniculata v. laxior, Caulerpa prolifera, Udotea petiolata, Dasycladus clavaeformis and by sponge Calix nicaeensis; in the Thyrrenean Sea by Laminaria rodriguezii, Cystoseira spinosa, Neurocaulon grandiflorum, Fauchea repens, Halymenia dichotoma, Callymenia reniformis and by the sponge Axinella cannabina. The environmental factors which determine these different facies in the circalittoral region of the two Mediterranean Basins are chiefly the temperature, the light intensity and the sedimentary rhythm.     

Proposta Di Una Scala Di Differenziazione Delle Gemme Fogliari Del Pioppo Utile Per Gli Interventi Antiparas Sitari

Abstract

A poplar leaf-bud differentiation scale suggested for the pest control treatments. – After having pointed out that also in Poplars the severity of the transplanting crisis and of several pest attacks is in relation to the development stage the leaves are in, the Authors suggest a differentiation scale of the leaf-buds particularly useful for the pest control treatments.     

Limnological Aspects of Two Tropical Crater Lakes (Lago Biao and Lago Loreto) on the Island of Bioko (Equatorial Guinea)

The limnology of Lago Biao and Lago Loreto, two tropical crater lakes on the island of Bioko, was investigated for the first time in January of 2002. Lago Biao fills a caldera at 1750 m altitude and is 18.5 m deep. This lake was characterized by low conductivity (11.6-13.3 S cm^–1), low pH (5.9-6.2), an oxycline between 6 and 10 m depth (90-27% saturation), and a Secchi depth of 5.5 m. Dinoflagellates, desmids, and green algae dominated the phytoplankton community. The rotifers Anuraeopsis fissa, Polyarthra indica, Trichocerca simoneae, and T. similis were most abundant above or in the thermocline. During the day Tropocyclops prasinus tjeefi and Chaoborus cf. ceratopogones concentrated in the oxycline, whereas Daphnia laevis was most abundant between 0 and 4 m depth. In contrast, L. Loreto is 82 m deep and probably fills an explosion crater (maar) at 1050 m altitude. The lake had a turbid, yellowish appearance and a Secchi depth of only 0.6 m. Oxygen content dropped from 121% at the surface to 6% in 10 m depth. The pH declined from 9.15 at the surface to 7.4 in only 2.5 m depth and became acidic at approximately 15 m depth. One species of cyanobacterium, one dinoflagellate and one green alga dominated the phytoplankton and together reached densities of 12 100 cells ml^–1. Only one rotifer (Brachionus angularis) and one copepod (Tropocyclops prasinus tjeefi) species colonized the open water. Intact algal cells and zooplankton specimens were encountered near the bottom.