<P> In monocot seeds, the embryo's radicle and cotyledon are covered by a coleorhiza and coleoptile, respectively . The coleorhiza is the first part to grow out of the seed, followed by the radicle . The coleoptile is then pushed up through the ground until it reaches the surface . There, it stops elongating and the first leaves emerge . </P> <P> When a seed germinates without undergoing all four stages of seed development, i.e., globular, heart shape, torpedo shape, and cotyledonary stage, it is known as precocious germination . </P> <P> Another germination event during the life cycle of gymnosperms and flowering plants is the germination of a pollen grain after pollination . Like seeds, pollen grains are severely dehydrated before being released to facilitate their dispersal from one plant to another . They consist of a protective coat containing several cells (up to 8 in gymnosperms, 2 - 3 in flowering plants). One of these cells is a tube cell . Once the pollen grain lands on the stigma of a receptive flower (or a female cone in gymnosperms), it takes up water and germinates . Pollen germination is facilitated by hydration on the stigma, as well as by the structure and physiology of the stigma and style . Pollen can also be induced to germinate in vitro (in a petri dish or test tube). </P> <P> During germination, the tube cell elongates into a pollen tube . In the flower, the pollen tube then grows towards the ovule where it discharges the sperm produced in the pollen grain for fertilization . The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants . </P>

Where does germination of a pollen grain occur