Andromonoecy and fruit set in three genera of the Proteaceae

It has been suggested by some authors that the low fruit to flower ratio in some Proteaceae is due to andromonoecy, while others, looking particularly at Banksia , have not been able to find evidence for male flowers in the inflorescences. Stirlingia latifolia, Xylomelum occidentals and X. angustifolium are clearly andromonoecous, while no evidence for this condition could be found in Brabejum stellatifoliutn. Production of fertile fruit is related to andromonoecy in Xylomelum and S. latifolia but not in Brabejum. It is unlikely that all-encompassing solutions will be found to what initially seem to be widespread traits in the family, especially in regard to pollination biology, as the genera in the family occupy widely different environments and have very diverse ecological ranges.     

Lactate Dehydrogenase Isozymes, Gytochrome Oxidase Activity, and Muscle Ions of the Rattail (Coryphaenoides sp.)

SYNOPSIS. Investigations into the behavior of molecules in organismsoccupying unique environments may provide a better insight intothe functions of these same molecules in organisms from morecommon habitats. An organism well suited for such analyses isthe rattail (Coryphaenoides sp.), a deep-sea teleost. The photoreceptorcells of the retina are predominantly rods. Although the lactatedehydrogenase A₁, and B₄, isozymes are present in this fish,the E₄ isozyme (found in the retina of many teleosts) is absentin the rattail retina. The rattails possess a lower cytochromeoxidase activity than shallow water fish. The sodium concentrationis higher, and the potassium concentration lower in the rattailas compared with surface marine fish. The patterns of molecularsynthesis and concentrations in the rattail may be related tosuch factors as light intensity, hydrostatic pressure, and temperaturewhich exists in the deep-sea environment.     

Effects of neighbouring vegetation on eucalypt seedlings at two sites subject to different levels of abiotic stress

Abstract In spite of numerous studies on the effect of nutrient levels and/or standing crop on the intensity of resource competition the debate has not been resolved. Field studies that have used natural productivity gradients have generally supported the argument that competitive intensity and resource availability are positively correlated, whereas studies that have used artificial resource gradients have generally refuted the same argument. Here we report the results from study in which both approaches were used within the same system. We studied two species of eucalypt that occupy contrasting parts of the same landscape: Eucalyptus camaldulensis, found mostly along creek lines and in valleys with deep alluvial soils, and Eucalyptus microcarpa, found on hillsides and ridges with shallow soils. We studied the response of seedlings of the two species to the combined effects of competition and manipulated nutrient levels in a glasshouse experiment, and also investigated their responses to removal of neighbouring plants in the field. Eucalyptus microcarpa was less responsive to increased resource availability, which is consistent with one of the principal assumptions of Grime’s C‐S‐R model. In the glasshouse experiment both species of eucalypt responded in a qualitatively similar fashion to the combined effects of resource availability and competition: release from competition resulted in increased growth, but only in pots that received additional resources. In the field we found that neighbouring vegetation could severely limit the establishment of E. camaldulensis but the removal of neighbouring vegetation did not affect the performance of E. microcarpa seedlings. Eucalyptus camaldulensis seedlings suffered high levels of damage from herbivores. Our results thus generally support the predications of the C‐S‐R model, however, they indicate that the effects of competition and herbivory may be heavily confounded.     

Pollen presenters in the flowering plants–form and function

Pollen presenters are specific floral structures, other than anthers, from which pollen is distributed for cross fertilization between flowers. They occur in only five families of monocotyledons and 20 families of the dicotyledons. Presenters in 15 families are described here. In the largest plant family (Asteraceae) all taxa have pollen presenters, while in others (e.g. Myrtaceae) they occur in only some species in a few genera. Most presenters are associated with the gynoecium and there is a wide range of forms involving hairs or outgrowths of the stylar tissue. Despite the placement of self pollen close to the stigma most taxa are outcrossing and avoid self fertilization by protandry, with the stigma being covered at anthesis, or by precise placement of pollen so that is does not contact the stigma. Likely selective advantages in the development of pollen presenters include greater accuracy in pollen transfer than in the normal anther to stigma movement and avoidance of interference between male and female organs in the flower. In some groups there is enhanced ability for female choice because effective pollen delivery enables a choice from among many pollen grains, while in others pollen presenters enhance male reproductive success. Study of the pollination biology of plants requires a knowledge of which plants have pollen presenters and a full understanding of the structures in the flower which are associated with the pollen presentation action.