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Abstract. Normally growing lily (Lilium longiflorumThunb.) pollen tubes cultured in standard sucrose medium display a relatively steady tip-growth pattern and a rather even pectin sheath in the cell wall. In an attempt to better understand pulsatory growth, observed in some species, e.g., Petunia, and its possible role in causing the formation of thickened cell wall rings, we have imposed marked fluctuations in the growth-rate of lily pollen tubes. The appropriate growth-perturbing conditions were achieved by modulating the medium osmolarity or by applying caffeine, a non-turgor inhibitor, in a specially designed incubation chamber with a controlled medium flow. The relatively non-esterified pectin deposition in the wall of the growth-interrupted pollen tubes was detected by immunofluorescence microscopy using a monoclonal antibody, JIM 5. The observations show that the periods of stow or inhibited growth correspond to the times when the thickened walls are deposited. Since the growth fluctuations were induced by both turgor-and non-turgorrelated means, the proposed endogenous regulatory role of turgor pressure is questioned. Other factors, such as the tip-focused Ca 2+ gradient which was demonstrated by ratiometric ion imaging, and the alteration in the extensibility of the cell wall, which correlated with pectin esterification/de-esterification, emerge as candidates for the regulation of growth fluctuations.

Investigations were carried out to correlate pollen viability, assessed on the basis of a fluorochromatic reaction (FCR) test, with pollen vigor, assessed on the basis of the time taken for in vitro germination in pollen grains subjected to high humidity (>95% RH) and temperature (38 °C) or storage stress of Nicotiana tabacum, Agave sp., Tradescantia virginiana, and Iris sp. Both high RH and temperature, as well as storage stresses, affected pollen vigor before affecting pollen viability. The results are discussed in the light of available data on the viability and vigor of stressed pollen and of aged seeds. The need for consideration of pollen vigor, particularly in stored pollen, the inadequacy of the methods presently used, and some of the methods suitable to assess pollen vigor are elaborated.

Production of stigma exudate per flower of Petunia hybrida is about 200 μg. The effect of light, temperature, metabolic poison and emasculation on the production of the exudate at different ages of the bud has been studied. The presence of a thin film of water below the stigmatic exudate has been demonstrated. Physical properties of the exudate such as relative viscosity and surface tension have also been determined. Chemical analysis of the stigmatic fluid showed that it consists primarily of an oil, sugars and amino acids. No protein could be detected. It also contains no acid phosphatase.Behaviour of the pollen from its deposition on the stigmatic fluid until it germinates on the stigma surface has been studied in vivo and also with the aid of an "artificial stigma".The role of the stigmatic fluid in pollination has been determined.