Cross-Section of a gymnosperm root showing secondary growth in the stele and Periderm formation in the cortex. Lecture Directory Sexual Reproduction Conifers produce Microsporangia and Megasporangia in Cones. Each Microsporophyll contains two Microsporangia . Each Microsporangium. produces hundreds of Microspores . These develop into Pollen Grains .
Pollen grains are multicellular and constitute the Microgametophyte .
There is a Generative Cell that produces two Sperm , and a Tube Cell that produces the Pollen Tube . There are some additional cells which do not contribute directly to the reproductive process. The mature Microgametophyte develops a pollen tube which delivers the sperm to the archegonia. At this point the sperm are released and fertilization occurs. The Microgametophyte thus has an Endosporic developmental phase and an Exosporic phase .