Maize pollination

Female flowers have extended the stigmata (silks) through the husk exposing them to the air. Male flowers, beginning first from the oldest florets, have extended anthers emerging and filled with pollen grains.  With a drop of relative humidity, the oldest anthers will open at the lower tip, releasing the pollen grains. The grains are sufficiently dry to be viable and yet float with the slightest of a breeze.  Some claim corn pollen can travel ½ mile in 15 minutes with sufficient wind but considering all the variables, i.e. genetics, relative humidity and amount of wind, it becomes difficult to generalize.  Seed producers, attempting to produce pure hybrids are well aware of the influence of pollen distribution. 
 
New corn pollen has a light yellow color but as it ages and desiccates in dry air it becomes dark yellow. Pollen will germinate when moistened by growing a germ tube. Pollen landing on the silk hairs (trichomes) produce enzymes that allow penetration of the germ tube into the silk.  Nutrition in the pollen grain is sufficient to grow about ¾ inch (2 cm). Nutrition from the silk is needed to allow continued growth down the several inches of silk channel to the ovule.  Although several pollen grain may initially penetrate the silk only one usually is allowed to reach the ovule, as the silk channel basically collapses as the germ tube progresses. Pollen grain penetration of a silk occurs within 5 minutes but germ tube growth to the ovule may require 40-60 minutes.
 
Once the germ tube reaches the micropyle of the ovule, the ovule causes the germ tube to burst, releasing the sperm. One sperm cell migrates to the egg cell with its monoploid nucleus fusing with the monoploid egg cell nucleus to form a diploid zygote.  The other sperm nucleus enters the central cell, fusing with its two monoploid nuclei forming a triploid endosperm.
 
This rather complex process of pollination leaves plenty of opportunities for things to go wrong which will be discussed in upcoming blogs.