Germination and storage trials were carried out with pollen of several rose varieties . The pollen grains germinated well in a 15%, sucrose solution with 40 ppm boric acid . Staining the pollen with a 0 .1 tetrazolium solution and standardizing the degree of colour at which the pollen grains are counted as viable, provided a good viability estimate, simpler to carry out than in vitro germination . Germination capacity and staining ability of the pollen were greatly impeded -about halved -by dehydration during storage in desiccators at low humidity . This effect could be corrected by humidifying the pollen beforehand for about one hour, though this pre-treatment increased the percentage of germinated pollen grains more than the percentage stained . There was no difference between the two percentages in fresh or in deep-frozen pollen .Pollen stored at 1 °C and high relative humidity soon lost its germination capacity ; between 0 and 20°" humidity a considerable proportion of the pollen remained viable for 9 months and longer . Storage for the same period in vacuum-sealed glass tubes at -24°C maintained viability as well or better and would probably prolong it further . Some of the cold-stored pollen induced a reasonable seed set after one year, a low seed set was obtained even after two years of storage at I °C and low humidity .

No abstract