Cotton "ginning" refers to the process of extracting fibers from cotton seeds. Seeds are removed from the cotton boll by hand or machine and processed into short lengths called "straw." Straw is then fed into a gin where it is compressed and spun into long threads called "yarn." These threads are used to make fabrics such as T-shirts, sheets, towels, and jeans. Ginning reduces the seed's weight so that more can be harvested from each plant. The extraction of fiber from the seed is done using chemicals which destroy the protein structure within the seed causing the fiber to fall out when washed. In North America, most cotton is ginningned before it is sold as raw cotton. Before the introduction of chemical pesticides and herbicides, farmers relied on birds for pollination. Because pollen is heavy and plants don't produce as much pollen when they're not open, farmers needed only about half as much cotton as they do today. This left more room for error and less need for industrial-scale farming. However, because cotton is vulnerable to pests and diseases, it must be protected with pesticides and herbicides.