When corn kernels are planted in moist soil, they absorb moisture and swell. This activates enzymes that digest and move nutrients to the developing embryo. These nutrients are found in the mass of stored food called the endosperm. The endosperm is about 90 percent starch and 10 percent proteins, oils, minerals, etc.
The embryo is actually a miniature plant with the kernel. It has a radicle (first root) and a plumule (five to six leaves). Growth begins with the emergence of the radicle from the kernel. This is followed shortly by the emergence of the plumule. A tubular modified leaf called the cleoptile, commonly known as the "spike," covers the plumule and protects it as it penetrates the soil surface.
Approximately 100 to 150 GDDs (heat units) are required for the cleoptile to emerge from the soil. Once this occurs, sunlight causes the cleoptile to split open revealing the first leaves of the corn plant. With adequate moisture and warm temperatures, emergence can occur in as few as five to seven days.
A cool and dry soil tends to preserve seed health and viability but delays emergence. As long as the soil is cool and dry, the germination process is not initiated. The seed remains dormant, and is basically still in storage.
Once the soil is moist enough for the seed to absorb water, however, the germination process can start, even at temperatures below 50 F. Under these conditions, the process will take time because cool temperatures slow the uptake of water into the seed.
During this lengthy germination period, the seed is vulnerable to chilling injury, fungi and other early season threats that can affect its health.
