Heterostyly inPrimula. 3. Pollen water economy: a factor in the intramorph-incompatibility response

Summary The pollens from pin (long-styled) and thrum (short-styled) flowers ofPrimula differ markedly in water economy. While pin pollen is little affected by atmospheric humidity, the germinability of thrum pollen in liquid medium is sensitive to the conditions experienced during the immediately preceding period, being depressed when the grains are partly desiccated, although capable of being restored with subsequent controlled rehydration. The tubes produced by incompletely rehydrated thrum pollen show abnormal growth forms, suggesting that the effect is on the membranes of the vegetative cell, a conclusion supported by observations on membrane state using the fluorochromatic reaction. Thrum pollen stripped of part of the material carried in the cavities of the exine by rinsing with a lipid solvent loses much of its capacity for the uptake of atmospheric water, indicating that, in this morph, some factor facilitating hydration is transferred from the sporophytic parent during pollen maturation.Implications of these differences in the physiology of the pin and thrum pollens for the functioning of the intramorph-incompatibility system are discussed.