Cells

Monday, December 19, 2011

When the pollen lands on the stigma it begins to grow. Each grain develops a tube which grows down the style into the ovary. The tip of this tube carries two pollen cells to be released into a ovule which also contains two cells. One pollen cell joints with the egg cell to create the new seed embryo and the other two cells join to create the food supply, rather like a placenta. The two parts are stored together in the seed coat. When a bee visits a flower, rummaging for nectar and pollen which it eats, it carries some on its body to the next plant it visits. If the next flower species is too different, the pollen tube will not grow on the alien stigma, so if the bee travels from a thyme flower to a marjoram flower nothing happens. But if the plant is the same variety or very near, cross fertilization will occur. Sometimes this creates interesting new varieties but it can also create muddy blends. This is the reason fennel and dill should not be planted near each other as cross-fertilization creates a seed without the clear flavor of either parent.