Progesterone. Print | Email article to a friend | Last updated: January 14, 2015. Progesterone is a hormone released by the corpus luteum in the ovary. It plays important roles in the menstrual cycle and in maintaining the early stages of pregnancy. It may also be involved in the growth of certain cancers.
Maple helicopters fall before the leaves drop from the trees. Maple trees (Acer spp.) produce winged seeds called double samaras, which twirl to the ground in late summer or early fall. They resemble helicopters in motion, earning them the common name of helicopters or whirligigs.
Many deciduous trees, like oaks, beeches, and maples, have instantly-recognizable seed pods (acorns, etc.) that release from the tree on a yearly basis. Because of the ease of obtaining their seeds, these types of trees make great choices if you're aiming to grow a bonsai tree from the seed.