The nectar-gathering animals disperse pollen at the same time. Foraging bumblebees collect pollen on tiny hairs while they bump around in flowers drinking, and deposit that pollen at the same time as they buzz among flowers. Then they go one further by scraping some collected pollen into tiny baskets, corbiculae, on their rear legs. Once home, the bees store the pollen in pots they make out of wax, keeping it to eat on rainy days.
In allowing plants to have sex at a distance, pollen, and ultimately flowers, led to explosive diversification, turning a brown planet green and then red, yellow, white, orange, and all the rest. Pollen diversified too. In the 300,000 pollen-bearing plant species on Earth, there are 300,000 different forms of pollen. The great variety in colors, shapes, and textures of the grains has evolved in accordance with each plant's biological particulars. Beetle-pollinated plants tend to have smooth, sticky pollen, the better to adhere to the lumbering beetles' backs. Plants pollinated by fast-moving bees or flies may have spiny pollen that lodges easily between the insects' hairs. Plants pollinated by bigger animals, such as bats, sometimes have bigger pollen, though not always—perhaps not even most of the time. In the details of pollen's variety, more remains to be explained than is understood.
The most recent story in the history of pollen is recorded not by the successes but by the failures. The air, however clear, is full of unsuccessful pollen, drifting in eddies of wind. Billions of grains reach the stratosphere. Even now, as you read, a few grains may rest on your hands or face, or on your cat. Pollen settles and accumulates in sediment, layer after layer, particularly at the bottoms of lakes and ponds.
In those layers, where decay is slow, pollen constitutes a history book far outlasting the plants that produce it. Grass pollen in sediment means grasslands, pine pollen indicates pine forests, and so on—an encyclopedia of detail spelled out in the mud. Palynologists take core samples of lake-bottom layers to examine shifts in the species of plants from one layer to the next. Collectively such chronicles of changing plant life can span thousands of years or more.