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.
Generally, maple tree seed that ripens and drops in the spring (April/May) do not need stratification and should be planted immediately. Maple seed that drops in the fall needs stratification. Sugar maple drops its seeds in late summer/early fall, so those seeds must be stratified before they will germinate.