Does a pine need a second tree?

A Pinus tree and a pair of Cycas trees in wind: winged pollen leaves male cones, drifts to exposed ovules, and a pollen tube grows to the archegonium; switching species shows one tree with both cones versus separate male and female trees.

Fertilise an ovule on a Cycas female tree, then on a lone Pinus tree, and explain which needed a second tree.

Pinus has male and female cones on different trees.

• Gymnosperms are heterosporous and make haploid microspores and megaspores, inside sporangia borne on sporophylls. The sporophylls spiral along an axis to form loose or compact strobili (cones).
• Cones with microsporophylls and microsporangia are male (microsporangiate) strobili. Each microspore becomes a male gametophyte reduced to a few cells, the pollen grain, which develops inside the microsporangium.
• Cones with megasporophylls carrying ovules (megasporangia) are female (macrosporangiate) strobili. Pinus bears male and female cones on the same tree; in Cycas, male cones and megasporophylls are on separate trees.
• One cell of the nucellus becomes the megaspore mother cell. The nucellus wrapped in its protective envelopes is the ovule.
• The megaspore mother cell divides by meiosis into four megaspores. One of them, still inside the megasporangium, grows into a multicellular female gametophyte bearing two or more archegonia, and this gametophyte too stays inside the megasporangium.
• Unlike bryophytes and pteridophytes, neither gametophyte of a gymnosperm lives independently; both stay within sporangia on the sporophyte.
• Pollen grains released from the microsporangium are carried by air currents to the opening of the ovules. A pollen tube carrying male gametes grows towards the archegonia and releases them near the archegonium's mouth.
• After fertilisation the zygote becomes an embryo and the ovule becomes a seed, which stays uncovered.

Teaching this idea? Put the simulation on your own page or LMS with this code.