Fulfilling my obligation
I don’t know why I feel a sense of moral obligation to write about corn every summer, and especially about the process of fertilization in that organism, but I do. Perhaps it is because so many of my students know so little about the plant and about the process. Not only are many unaware that corn is monoecious, a single plant has both male and female parts, but many more are clueless as to what these parts are called, where they are, and how corn plants actually do it. So indulge me as I discharge my obligation to the thinking world. To begin with, the tassel at the very top of the plant is part of the male reproductive system and is responsible for the production of pollen. Pollen transports sperm to fertilize the egg which resides within the kernel; but how does the former reach the latter which is sequestered deep within the ear? The solution is that each developing egg grows, from within its protective and nourishing kernel, a tube which we call silk. The silk connects the egg, within the kernel, to the outside world. When a pollen grain, released from one of hundreds of anthers on the tassel, lands on the tip of a piece of silk it will germinate and grow a pollen tube which will allow the male reproductive nucleus access to the egg, and voilá, fertilization will be achieved. It is in this way that an ear of corn may correctly be viewed as so many corn-babies, each resulting from the fertilization of an egg cell by a sperm cell. The images below show a mature tassel; a closer view of a single tassel spike, with all of its colorful anthers; an ear of corn with its characteristic tuft of silk; and an undeveloped ear which has had its husk removed, allowing you to see that each developing kernel has a tube of silk emerging from its surface. So, what about the last three images? What do they have to do with corn reproduction? The interesting machine is a detasseler, a high-clearance tractor which supports eight rotating blades which are adjusted to ride just below the lowest point of the tassel. And, why would anyone want to detassel a field of corn plants? To produce, in a very controlled way, a hybrid corn crop of course. The key to producing hybrid plants is in the planting of the field and in the selective detasseling of individuals. The field is sowed to two varieties, every fifth row is planted to a variety that will act male while the other four rows are planted to a different variety that will act female. The plants in the female rows are detasseled and then harvested later as the primary crop (the tasseled, male, plants will be harvested as animal feed). Detasseling produces the characteristic notched pattern of fields planted in this way that you may have seen while traveling along an adjacent highway. Because of variation in the height of individual plants, the process of machine detasseling is only 80-90% effective and the remaining tassels must be removed by hand. You may be aware that a large number of young people across this country and across the globe are put to work for a short period of time each summer walking the fields in search of tassels which have been left behind and which they then remove by hand. Check out this article from Modern Farmer Magazine which describes the subculture of teen-detasselers in St. Joseph County, Michigan; and thanks to Lori Potter at potterspix for the nice shot of a crew of Nebraska detasselers. Now, the answer to the question of why one would want to produce hybrid corn is, hybrid vigor, which is both self-explanatory and a topic for yet another day.