RATES OF POLLEN DEPOSITION AND REMOVAL IN MYOSOTIS-COLENSOI

1. The flowers of Myosotis colensoi are protogynous. The stigma is acc essible for pollination for several hours before pollen is presented. One or two days after a flower opens, scales at the mouth of the corol la tube change colour, signalling the start of a protracted post-polli nation phase. Flowers in this phase present neither pollen nor recepti ve stigmas and they are avoided by the principal visitor - a tachinid fly. 2. Hand pollination of protected stigmas shows that they remain r eceptive throughout the life of the flower. During favourable weather, however, pollen is deposited on most stigmas before the anthers dehis ce. The effective female phase is thus shorter than the nominal period based on either the period of stigma receptivity or the end of the pe riod before pollen presentation. The effective male phase is much long er, requiring as many as 12-14 separate visits to complete. 3. Pollen presentation is staggered because the five anthers dehisce sequentiall y over several hours. This process extends the period over which polle n is removed. 4. Periods of poor weather alter the presentation schedu le and pollen removal and deposition rates, lengthen the effective pha se durations and cause a partial temporal overlap in sexual functions. These results are discussed with reference to theories of sexual sele ction.