Corn Silk, water and history
Silk, the stigmata of the female flowers of corn, grow from each flower in the lateral branches of the corn plant that we call a corn ear. Extension of the the silk growth is powered by the water pressure as those molecules migrate via xylem cells through this stem tissue of the ear shank. Water availability during this time is critical to this exposure of all the silk, each leading to a single flower in the ear. We can thank corn’s history for this interaction.
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.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.