Corn Insufficiently Pollenated
Each individual ovule must be fertilized with the nucleus of a pollen grain. The so-called silk of the corn consists of thread-like pistils, each of which leads to an ovule. The pollen, produced in the tassel, sifts through the air in great quantities, but sometimes it fails to reach all the threads if the corn silk. In that case a defective ear is produced as shown in this picture.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 3 Chapter 3