Pollen viability is known to decline, sometimes rapidly, with age and exposure to environmental stresses. Because of the potential impact of nongenetic factors on the ability of pollen to fertilize ovules, researchers conducting hand-pollinations should attempt to control the freshness or viability of pollen used. We surveyed hand-pollination experiments published in seven major journals from 1980 until mid-1994, collecting data on the purpose of the experiment, the degree of care taken to ensure pollen viability, and the degree of care taken to ensure stigmatic receptivity. Fewer than one-third of the papers reported any consideration of pollen freshness or viability, whereas over one-halfmade some mention ofstigmatic receptivity. Pollen freshness or age was mentioned more frequently for some types ofexperiments than for others. Experiments attempting to compare performance of different donors are especially susceptible to error when donor pollen is not treated equally or otherwise controlled for viability. We discuss strengths and weaknesses oftests to measure pollen viability, and experimental protocols to reduce differences in pollen condition across donors.Darwin's concern with the effects of cross-and selffertilization in plants led him to conduct many controlled pollinations in which he collected pollen from particular donors and transferred it to the stigmas ofrecipients (1876, 1877). Controlled pollinations remain a mainstay ofmany investigations today. The questions are diverse, but many still involve comparing the performance ofpollen donors. Classical issues, such as inbreeding effects and the functioning of incompatibility systems, are still of interest, but the recent emphasis on the important role of male function in floral evolution has brought new questions with it: sexual selection and "female choice," resource vs. pollen limitation of seed set, gametophytic selection, etc. We lump all of these issues under the heading of "evolutionary ecology." As documented by Keams and Inouye (1993), publishing activity in pollination biology is soaring, and many of the recent surge of papers use controlled hand-pollination. Although mostly done in the field or in greenhouses with only modest control of the climate, this work is founded on the assumption that differences in the performance of different pollen donors are genetic in origin.There has also been progress in the study of pollen grain physiology. The issue of pollen viability has received attention, and it is now apparent that there is great variability among species in the effective life spans of pollen grains (see, for example, Table 5.2 in Stanley and Linskens [1974] or Tables 4.1 and 4.2 in Shivanna and Johri [1985]). Storage conditions, especially temperature and relative humidity, can have strong effects on the competence of pollen (Johri and Vasil, 196 I; Stanley and Linskens, 1974; I Manuscript Shivanna, Linskens, and Cresti, 199Ia). Workers in this field have devised various tests for pollen viability and vigor, and have used them to d...
