A grain of pollen contains a sperm cell, surrounded by walls to keep it safe. The inner wall, or intine, is less sturdy and made of cellulose, but the outer wall, or extine, is made up of a very stable and tough polymer called sporopollenin. It is this outer wall which forms the distinctive shapes and external structures that help us tell different types of pollen apart. For example, the large red pollen grain in the center of the image (Cucurbita pepo – which includes pumpkins and squash) and the round grain with multi-colored protrusions at the bottom right (Ambrosia spp. – ragweed) have spiky structures. Others have net-like, or reticulate, patterns, like the orange and green Scots pine (Pinus sylvestris) pollen grain near the top left. The shape and size of pollen can give clues about how that plant gets pollinated. Plants which are pollinated by insects (entomophilous plants) tend to have heavier and stickier pollen grains, while plants whose pollen is carried by the wind (anemophilous plants) usually have lighter, non-sticky pollen. The red and green pollen grain that resembles a barbell is one of these wind-borne pollens, and was featured in last week’s Instagram image – follow us @SITN_harvard to learn more about this pollen grain!

To read more about the science of pollen, click here.

Artwork generously contributed by DWP.