In most pollen-producing plants, a grain of pollen successfully completes its journey when it travels from the male portion of a plant specimen to the corresponding female portion. Ideally, it finds its way to an entirely different plant to increase outcrossing borne from crosspollination. That's not always a hard and fast requirement, however, although it's important to note that many plant species have ways to prevent a particular plant from pollinating itself. Some are even genetically self-incompatible.
Once a grain of pollen reaches the plant's female portion, in most cases an ovule, one of the lucky sperm (typically out of two) lodged within the pollen will fertilize the egg cell inside. After fertilization occurs, the ovule will gradually develop into a seed, and that seed will transport its embryonic plant to a new home.
Plants that follow this basic reproductive path are known as gymnosperms. Trees that have pinecones and similar reproductive structures, as is the case with most conifers, are examples of gymnosperms. Let's take a closer look at conifers, the most numerous and widespread gymnosperms on Earth today, and pines in particular, since they're some of the most familiar species.
Pinecones generally come in male and female varieties, and they can be all sorts of shapes, textures and sizes, depending on the species. One makes the pollen, and the other receives it. Once a pollen grain arrives at an ovule -- usually adhering with the help of a sticky substance produced by the female pinecone -- it absorbs water, germinates and starts slowly growing a pollen tube in order to place the newly generated sperm inside. Fertilization occurs, and a seed eventually forms. The length of time it takes for the overall process to complete itself varies greatly; in many pine species, the pollination process takes more than a year from start to finish. Once it's finished, the seed is liberated from the cone, to travel on its way.
But although the development of the pollination process was revolutionary, it still had some kinks that could be worked out. On the next page, we'll take a look at the plants who whipped out the evolutionary iron and made the method that much more reliable.