Corn female flowers

Teosinte, the ancestor of corn, has lateral meristems at each node, producing about 10-20 female flowers in two rows attached to a narrow rachis and each flower with a long stigma protruding beyond the modified leaves that surround the flowers.  In most Teosinte species the male flowers develop from the apical meristem, much like a corn tassel.  As people selected for mutants that had more grain like corn, they also maintained the leaves (husk) that helped protect the ovules and, later, the developing grain from invasion by insects and pathogens.  It was also convenient as a wrap for cooking corn (tamales anyone?)
 
The ear of corn is composed of parent plant tissue and DNA surrounding a group of flowers attached to a central stem (rachis) we know as the cob.  Each flower has a single stigmata that we know as silk that extends beyond the outer leaves (husk). The silk tissue, husk, cob and the outer layer of cells of the ovules are parent plant material and therefore controlled by genetics of the hybrid plant.  Benefiting from the vast genetic diversity, breeders over the millennia selected for variants with different husk characters that met their specific needs.  Heavy insect pressure environments favored those with longer and perhaps thicker husk leaves.  Short season environments requiring quicker field drying the mature grain favored those with thinner and shorter husks. 
 
Silk growth also had to accommodate the husk length of husks in order to get exposure to pollen. Silk growth is largely a cell elongation process.  Like all cell growth, water pressure is needed to extend the silks, thus it is dependent upon the plant environment.  Genetics also is a significant factor that requires breeders to select for good silk extension even with drought pressure.  Timing of the silk emergence from the husks is also important because of the limited time in which viable pollen is available. Although the first silks to enlarge are the oldest at the bottom of the ear, those with a shorter distance, perhaps an inch from the bottom reach there first.