The effect of varying the number of pollen grains used in fertilization.

The number of pollen grains placed upon a stigma influence both the development of pollen tubes and subsequently the progeny which result from fertilizations by gametes from these pollen tubes. The first influence is demonstrated by reduced pollen tube growth rates when pollen grains are few in number. This may indicate direct effects of pollen tubes upon the stylar tissues or perhaps more complex interactions between pollen and style. The second and potentially more important influence of limited pollination is upon the progeny. This was demonstrated with studies on three species. In each case, variation among the resultant plants was greater when pollen was limited than when normal, that is excessive, pollen was used. The mechanism of this phenomenon is not certain, but our data indicate that it is not simply an artefact of variation in seed size.