Figure 122. This series of micrographs shows male and female gymnosperm gametophytes. (a) This male
cone, shown in cross section, has approximately 20 microsporophylls, each of which produces hundreds of
male gametophytes (pollen grains). (b) Pollen grains are visible in this single microsporophyll. (c) This
micrograph shows an individual pollen grain. (d) This cross section of a female cone shows portions of about
15 megasporophylls. (e) The ovule can be seen in this single megasporophyll. (f) Within this single ovule are
the megaspore mother cell (MMC), micropyle, and a pollen grain
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.
Reproductive Process The pollen's tube cell forms the pollen tube when it touches down on the female cone, through
which the generative cell moves to the female gametophyte through the micropyle. The pollen tube
grows and moves toward the female gametophyte over the course of about a year. One sperm nucleus
from the male gametophyte that contains the generative cell merges with the egg, while the other
degenerates. The embryo is created by the mitotic division of the diploid zygote, which is created
after fertilization of the egg. During the development of the seed, the scales of the cones are closed.
A seed coat, which originates from the female sporophyte, protects the seed. It takes another year or
two for seeds to develop. The female cones' bracts open when the seed is ready to be dispersed,
preventing the formation of fruit because gymnosperm seeds lack a covering
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.
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(credit: modification of work by Robert R. Wise; scale-bar data from Matt Russell)
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Clark, M., Choi, J. & Douglas, M. (2020)
Biology 2e , Chapter 32, -Pp.896-898, OpenStax,
https://openstax.org/details/books/biology-2e
