Coleoptile reaches the soil surface
Soon after the primary root breaks through the kernel pericarp, the embryo stem portion grows upwards. Enzymes in the cells assist in production of hormones and cell wall components need for the elastic cell walls to expand. Turgor pressure caused by adequate water infusion assists in cells growth, auxins assist in the geotropism guiding the growth towards the upwards, as the cells on the lower side of the shoot tissue elongate more than the upper side until growth is vertical. Initial elongation occurs in the mesocotyl tissue with the meristem at it tip, surrounded by the coleoptile, a short leaf tissue, functioning as a shield protecting the more delicate meristem tissue.
The meristem (growing point) in the mature seed already possessed the groups of cells that would elongate into the coleoptile, followed by other lateral groups of dividing cells for the first 5 or 6 nodes all near the tip of the meristem. The first node, furthest from the tip of the apical meristem is at the base of the coleoptile.
As the coleoptile reaches the red spectrum of daylight, hormonal molecules transmitted to the mesocotyl cause stoppage of the its cell elongation. Remaining growth upward comes from growth of the coleoptile. The second furthest node from the tip of the meristem now produces the initial first true leaf, usually a short leaf unwrapped from the coleoptile. With a little more time, the other 4-5 nodes around the meristem begin increasing cell division to eventually produce the next 4-5 true leaves in the young seedlings. These nodes from which the leaves derive, remain under the soil surface, compacted within a few inches of tissue. This underground tissue is sometimes referred to as the crown.
These are the processes of vigorous seed in conditions favoring penetrable soil of adequate temperature, oxygen and moisture with no chemical interference. These conditions are not always present for each seed.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.