One of my friends recently asked me an interesting question that most of us just take for granted. We know that four to five leaves of the corn seedling emerge, but the growing point remains below ground. How is it possible that the growing point “jumps to the top” over all those early leaves that came out first?
You’ve likely recently watched it happen again this year. It is an interesting phenomenon of Mother Nature. Here is an explanation from the botanical standpoint.
Most crop plants belong to either the monocotyledon (monocot), or dicotyledon (dicot) family. At germination, if only one leaf emerges out of the ground first, it belongs to the monocot family. If two leaves emerge, it belongs to the dicot family. Corn, wheat, rice, oats and barley are all monocots. Soybeans, peas and alfalfa are dicots.
When a corn plant emerges, the seed stays put. You can find it below ground while scouting to confirm planting depth. When a soybean emerges, the pair of cotyledons that emerge were the two halves of the soybean seed. A pair of unifoliate leaves then appear, followed by trifoliate leaves.
To the point
What does this have to do with growing points and leaves? If the growing point of a dicot plant that already has leaves gets destroyed, more growing points develop from the axils of the leaves. The plants branch. It happens in soybeans. Most monocots, like wheat, produce more tillers.
Corn was domesticated by man over more than 10,000 years to produce big ears, which were easy to harvest. It does not tiller much, and its growing point is very critical to its survival. So, the growing point is carefully protected by leaves below it.
Even though the growing point emerges later and appears above ground after four or five leaves, it really was always on top and originates all leaves until the tassel comes out.
The first leaf that emerges for monocots is the coleoptile. It pierces the ground and allows real leaves to follow. It protects young leaves as they try to get out. When corn seed germinates and the first four leaves emerge after the coleoptile, the growing point is still below ground, protected from the vagaries of weather.
Always on top
Even though it appears that the growing point is beneath the first leaves, in reality it is always at the top. Other leaves protect it until the tassel comes out.
The position of the growing point is critical for protecting the plant from above-ground damage. At first the growing point is located near the crown. At about V4, when there are four visible leaf collars, the stalk begins to elongate, and the position of the growing point rises over a few additional leaves.
The growing point is located near the top of the stalk tissue as internodes start to elongate and newer leaves develop until the tassel forms. During June and July, as corn approaches the reproductive stage, find the growing point by peeling back tissue at the top of the true stalk. How a corn plant develops is a true wonder!
Nanda is director of genetics for Seed Genetics Direct, Jeffersonville, Ohio. Email [email protected] or call 317-910-9876.