Germination of pollen of the dwarf mistletoe Arceuthobium americanum
Pollen of Arceuthobium americanum Nuttall ex Engelmann, a parasitic dwarf mistletoe of Pinus banksiana Lamb, in Manitoba, was germinated on media containing a range of concentrations of sucrose and salts. Highest germination levels occurred on 20% sucrose agar; addition of salts significantly depressed germination. Pollen germinability was below 5% at first but increased to near 50% as the season advanced. Mean germination differed significantly between flowers from 10 staminate plants but peaked at approximately the same times in association with increasing temperatures. Freezing night temperatures were followed by reduced germinability. The optimum temperature for in vitro pollen germination is close to 30 °C, whereas 40 °C impairs germination. Key words: parasitic angiosperms, microclimate, jack pine, reproductive biology.