Silk

I have always been fascinated to learn about what people don’t understand about the world around them. In my capacity as a biologist I have had ample opportunity to learn about the sorts of things folks simply get wrong. I have quite a number of stories I could tell to make my point but I’ll spare you and recount just one. Several years ago I was driving a group of students through the countryside on our way to a small nature preserve. These were biology students and, if I remember correctly, the intent of the field trip was to learn something about plant community structure. Along the way we drove past a farm and along the side of the road there was a bull standing in a paddock. For those acquainted with bull anatomy you’ll know what I mean when I say that this was very obviously a bull. The students all took in the massive specimen and as we passed one student remarked, “Gee, I wouldn’t want to milk that cow.” Each academic year a whole new crop of misunderstandings arise, thereby giving me fodder for explanation. During genetics laboratory we make use of specially cultivated ears of corn in discussions and demonstrations of genetics. I am always surprised by how much students do not know about corn. First, they do not know that corn plants are monoecious and each has both male and female reproductive parts. Second, although they are vaguely aware that the ear has something to do with female reproduction, they have no idea where the male structures are. [Every once in a while a farm kid will raise his or her hand to set the record straight.] The tassel, at the very top of the plant, is responsible for the production of pollen and is therefore part of the male reproductive system. Fine. Then I ask my students if corn plants have sex. After their initial shock at the way in which the question is phrased they think about it and immediately become confused. Sure the tassel produces pollen which carries 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 fact is that each developing egg grows, from within its protective and nourishing kernel, silk. The silk is a tube connecting the egg to the outside world. When a pollen grain 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 voilรก … fertilization is achieved. I was watching straw being baled down by the river. During a lull in the action I noticed that the corn was in silk. I thought this made for a nice image – I hope you will agree. You may click the image for a view with higher resolution.

Silk

27 thoughts on “Silk

  1. I don’t know about anyone else, but I would love to hear more of your stories derived from teaching over the years. If you’re afraid of offending anyone, write them under another anonymous blog. The tales you have to share, both good and bad, would be a most enjoyable read. Of course, I have the advantage of still having your voice stuck in my head. That does add something when I read your passages.

  2. Interesting conversation here, D. I had to pause to remember the word monoecious again. I haven’t used it for a while. I love to watch corn grow. Some of the older people in the community where I grew up held the belief that in order for corn to produce ears it was necessary to plant rows next to one another, and the entire process was helped along by regularly walking through the corn to help the pollen be carried to the appropriate places. I’ve never thought this could be required agricultural practice (to act like ‘bees’) but I always liked the story.

    • Cool … very, very cool. Isn’t it fascinating how many of the older traditions have a basis in scientific fact? Those plants would surely have benefited from folks walking the rows and thereby liberating the pollen. I’m sure practices such as this simply evolved through trial and error … what worked was past down through the generations, while what didn’t work was forgotten. D

  3. That’s such a beautiful photo … of a plant ready for sex … is that wrong? I love the image anyway … such fresh vibrant green … and a wonderfully fascinating mini-lecture David. You and Joanna are such a knowledgeable pair ๐Ÿ™‚

    • ‘Is that wrong?’ I don’t get it … what could be wrong in recognizing that plants engage in sexual reproduction? Few are able to detach themselves from the (human) social conventions that tell us what’s OK to think and talk about long enough to really consider that fascinating topic which Mr. Darwin said was Job #1 in the natural world – and that is, reproduction. Natural selection has fashioned so many different means of making babies – it’s a science all to itself. Anyway, I’m glad you enjoyed this foray into the intimate life of crop plants. D

      • ‘Is that wrong,’ referred to my question of … is that a plant ready for sex? Sorry for the confusion … I just wasn’t clear if that’s what the photo was showing ๐Ÿ™‚ Beautiful photo full of fresh green growth.

        • Oh … got ya. The image was of an immature ear which is why the strands of silk were sort of rigid. I doubt that fertilization would be possible at this point, even in the presence of pollen. As the silk matures however the threads lengthen and droop such that the mature ear looks like a woman with head of thick hair falling around her shoulders; it is at this stage that the pollen may germinate and begin its journey to the kernel within. D

          • I have recently been taking some shots of wheat and barley fields, so am now going to pay closer attention to their state of readiness for sex. Really fascinating David … as always.

  4. What a great image … my new desktop background! Dave, I have to tell you an enormous number of your images linger on my desktop. Katie is working on the Magic project this summer … a long term (corn genetics) she’s worked on at Purdue for several summers. Part of her job is to breed the plants in the field, placing approved pollen onto specific ear/silks …. we call her the corn sexologist! When the corn really started pollinating a few weeks ago, she was getting highly personal with a lot of ears and would come home incredibly sticky, covered with pollen, and complaining “I have corn sex all over me!” We told her, “But it’s for Science!”

    • Your story reminds me of the time we took the girls down to the creek for a swim. The water was warm and there was a bit of algae in the shallows. Molly emerged from a dip covered with the stuff and announced, ‘Biology!’ Tell Katie she’s following in some pretty big footsteps … Mendel, Morgan, Crick (Watson – who is he?), and McClintock (especially). What do they say … You (Katie, that is) Go Girl. D PS: I’m glad you enjoyed this image … sort of looked like a sea anemone to me!

  5. Beautiful photograph! It looks otherworldly, as so many of your photos do. It could be from under the sea, or an altogether alien world.

    • Yes. This was a young one, just producing its silk. The threads were fine, self-supporting, and didn’t droop. I thought the result looked something like an anemone. The threads appeared to wave in the nonexistent currents, eddying to-and-fro. I had some time on my hand to take this image while I waited for the guy baling straw to make his eastward pass down the field. Thanks for checking in. [I owe you an email … it’s on the list.] D

  6. Believe it or not, today I pondered questions like this, in relation to a staghorn sumac tree in a our garden. I believed these plants are either male or female (white or red flowers), but this year the flowers have changed from white to red.

    • You mean the entire plant flowered one color last year and then switched this year? I just looked it up and found that this species is dioecious, so you were right … clumps are either male or female. I wonder why an individual genetic unit would switch the color of its flower from year to year? I guess we can chalk it up to what we call ecophenotypic effects! Thanks for checking in. D

      • It was even stranger. The tree had some white flowers earlier this year (male as I learned from Dr. Google), and now (some) red flowers have appeared. I expected it to be either male or female, but not to change its “gender” in a season. The strategy would make sense though. We have grown some other trees from the main one (this tree grows like a weed anyway – you have to kill lots of them every day) – so our local population lacked the red ones. But how does the main tree know?

        • Long story … but, as it happens, for her doctoral research my wife studied sex allocation in Stinging Nettle (Urtica). Turns out that plants have a remarkable plasticity of sex expression. Some individuals may flower entirely female, others flower entirely male, while others flower a combination of the sexes. It would appear that the plant is able to ‘take stock’ of its nutrient reserves, and nutrient availability, and flower accordingly. Very small plants flower as males because doing to is not very costly and flowering as a male allows lots of cheap pollen production with a pretty good pay back if the pollen can get out and about the environment. Very large, healthy, and mature plants flower as female because they have the resources to do so – here, the reproductive potential is higher because genes go into known quantities. And, in between, plants flower as some combination of male and female. This all applies to Urtica … I wonder what’s going on with the Sumac? D

          • Very interesting – thanks! The “partly female” tree is the oldest in our “family”, thus most mature and – I think – very healthy (producing tons of these pesky stolons, I hope this is the correct term). So I expect it to turn into a 100% female plant next year! I will keep you updated!

  7. What a beautiful image. The black and lit shades of green are perfect contrasts. Have to admit that I did NOT know about the purpose of silk. I will never look at shucking a cob of corn in the same way!! ๐Ÿ™‚

    • Dam stuff, always plugs the drain in the kitchen sink. Thanks for complements on the image. It was taken with the SONY … the Nikon had to be shipped to NY for a shutter replacement relating to dust and oil on the sensor. I’m in a deep depression over it.

  8. It’s beautiful. While reading Jared Diamond’s “Guns, Germs and Steel” a few years back I became a bit more familiar with Corn. Farming has come a very long way over the many thousands of years. Now, here’s a thought regarding that student. He graduates and gets work on that very farm. Next morning the farmer spots him trying to do his work and says, “Errrrr John, that’s not an udder …”

    • Ha! Yes, I read Diamond’s book as well. If I remember correctly … the world is the way it is, geopolitically, because of the way it is, ecologically. Interesting idea. I also remember the book being much longer than it needed to be to get across this simple thesis. Anyway, thanks for painting a word-picture for me this afternoon! D

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