Explain how the pine life cycle in Figure 30.6 reflects the five adaptations common to all seed plants.
The ovule contains the megasporangium which gives rise to the female gametophyte; this structure remains protected within the sporangium and integument. Archegonia develop within each gametophyte, each containing an egg cell. Pollen is produced in the microsporangia of the male cones. Each pollen grain contains a generative nucleus, tube nucleus and two body cells. Pollen is delivered via the air (wind, usually) to the opening of the ovule (micropyle). The tube cell forms a pollen tube through which the sperm nucleus (derived from one division of the generative nucleus) is delivered to the ovule. After fertilization the embryo develops within the ovule and a seed is formed from the integument (seed coat), nutritive tissue (gametophyte) and embryo (next generation plant or sporophyte).