From Flower to Fruit
Pollination takes place in many different ways. Sometimes the pollen simply falls onto the pistil. More often, wind or insects aid the pollination. The pollen lands on the stigma of the pistil, which is usually either sticky or rough. There the pollen is held. It then begins to grow, each grain developing a tube which extends down the pistil to the ovules. Thus, if the style (the neck like part of the pistil) is long, the pollen tubes may also have to grow several inches long. Inside each pollen tube are two sperm cells, which by the growth of the tube are carried to an ovule. When a pollen tube reaches an ovule and grows into it, the sperm cells are released. One sperm unites with the egg cell of the ovule, and from this union a new plant grows. The other sperm unites with another cell in the ovule, and from this union the food supply for the new plant is thus, as a seed grows to maturity it contains a new plant and some food.
Around most seeds is a protective coat, which may become rather papery, as in the bean, or even very hard, as in the Brazil nut. While all these changes have been going on in an ovule, other changes have taken place in the flower. The petals have fallen, the stamens have shriveled, and the style and stigma have withered. The ovary has enlarged, and it continues to enlarge and change until it becomes a mature fruit sometimes soft and juicy like a tomato, sometimes dry like a bean pod, and sometimes hard like an acorn. In stone-fruits like the peach or plum, the outer part becomes fleshy and the inner part becomes hard. Only when this hard part is cracked open is the seed inside visible. From the pistil of a flower, with the aid of pollen from the stamens, seeds are formed inside the fruit.