Passage III

In Zamia (a genus of seed plants), males have pollen­ producing cones, and females have seed-producing cones. Pollination requires the movement of pollen from inside a male cone to inside a female cone, where multiple ovules are located and pollinated. The ovules then develop into seeds. Two students discuss the pollination process.

Student 1

In Zamia, 90% of ovule pollinations result from insect pollination; 10% result from wind pollination. No other pollination mechanism exists.

Zamia have mutualistic (mutually beneficial) relation­ships with insects. Weevils (a type of beetle) swarm male Zamia cones when these cones are releasing pollen. Upon entering the cones, the weevils become covered with the plant's sticky pollen. The weevils then visit the female Zamia cones. In the absence of weevils, the percent of ovule pollination in Zamia is about 10%.

Wind pollination is infrequent because Zamia pollen is large and heavy. Additionally, the openings into the female con s are aligned horizontally, so wind-borne pollen must be blown horizontally to enter these cones.

Student 2

Wind pollination and insect pollination each cause 50% of pollination events in Zamia ovules. Without wind pollination, the percent of ovule pollination decreases by 50%. Likewise, without insect pollination, the percent of ovule pollination decreases by 50%. If neither of these processes occurs, the percent of ovule pollination decreases by 100%

wind tunnel experiments show that the shape of the female zamia cones creats air currents that facilitate the horizontal movement of pollen into these cones. Additionally, male Zamia cones produce enormous quantities of pollen, a trait that is common only in wind-pollinated plants.

The students proposed 3 experiments using a natural Zamia population in an area with weevils and in which the percent of ovule pollination is normally 99% (see the table).