This short movie shows corn seeds germinating and growing in darkness (imaged with infrared illumination) over a period of a few days starting 36 hours after being planted in wet soil. Note that the root is the first part of the seedling to emerge from the seed. The seed on the left was planted with the embryo aligned with its root pointing down. The seed on the right was oriented with the embryo upside down. As the movie shows, the roots from both seeds grew down regardless of the initial orientation of the embryo. Also, when the shoots emerged they grew up from both seeds. The ability of the seedling to orient its growth occurs as a result of the process of gravitropism by which plants sense and respond to the direction of gravity. The time between images in this movie was 1 hour.
In darkness, as would be normal for seeds buried in soil, most of the food reserves in the seed are used to fuel seedlings to grow enough to reach the light so they may do photosynthesis. Through the process of gravitropism, seedlings are able to orient their roots in the absence of any light signals so they will grow down into the soil where they can find water and minerals for growth. The seedlings also use gravitropism to orient their shoot so they will emerge from soil where light will initiate the process of photomorphogenesis so the plants will be able to use the energy of light for photosynthesis and subsequent growth. Photomorphogenesis is the process during which leaves develop and become green. Movies showing more about the gravitropic response can be found in "Tropisms" section of the site. Movies showing the process of photomorphogenesis can be found under "Photomorphogenesis".