Question

why is it preferable for a plant to encourage cross pollination rather than self pollination?

Answer 1

Cross pollination includes variations whereas self pollination do not show such variation in characteristics.So,Cross pollination is ,more preferable than self-pollination.

Answer 2

By cross-pollination, the heterozygosity increases, the offsprings (Hybrid) are superior than the parental generation, which give higher production along with variation, a tool of genetic improvement. That's the reason cross-pollination is preferred over self pollination.Hope it helps to understand basic concept of Genetics.