02 January 2016

Cotton Blossoms

Cotton is nifty.  You may not know very much about it; I didn't, when I started working in crop science.  We have a lot of cotton plants growing in the Phytotron at NC State, and today at work I took some pictures of various stages of cotton flowers.
Cotton is a tropical perennial, and can live for several years and grow quite large.  Unusually for perennials it blooms in the first year on new growth, so we culture it as an annual.  Typically for a perennial, it is slow to germinate and seedlings are not vigorous.  It develops branches at each leaf node on the main stem, and a boll develops at the leaf nodes along the branches.  You get more cotton with more branches, but the more branched the plant is the harder it is to grow as a row crop, the more likely the leaves on the lower branches won't get much sunlight, and thus the less likely that the lowest branches won't ultimately develop bolls.  Most of cotton breeding has consisted of managing these variables: stronger seedlings, taller, straighter plants with upright branches that can capture enough sun to produce multiple bolls in a single growing season.  A researcher here at NC State is even trying to manipulate the shape of leaves at different levels of the plant to allow more light through the top of the canopy while capturing as much as possible at the bottom.
Here we see some little wee leaves and blossoms just getting their start in life on a new stem.  Your T-shirt and jeans start here.

Another day or two goes by and the flower bud becomes clearly visible.

On the left is another flower bud.  I could not find anything between the stage there on the left, and the fully open flower on the right.  Note the fully open flower is white with widely separated petals.  This will last for just a few hours.

This is just a few hours later.  Still white, but the petals are beginning to fold up.

A few hours later still.  The petals have all folded.  Note that the flower is open for just a few hours of a single day.  Still white, though.

Here just the barest hint of pink is beginning to show up at the edges of the petals.

Just a bit more pink.

Now we have quite a nice slightly pink flower.  This flower is done; it's been pollinated by now, if it's going to be, although pollination isn't necessary to get a boll.  

A bit more time passes, a bit more pink.

As you can see the petals are starting to wilt and sag.

Even as it wilts this a really pretty flower.  They have a nice aroma, too.

The last stage.

Suitable for dried arrangements.

The dried flower separates from the boll.

And the green boll begins to emerge.  The boll at this stage is referred to as a square.

Okay, this is pretty much the same stage as before, but it's a nice picture.

The square expands.

At this point I think the square looks like a lime.

The square opens...

And the boll emerges!

And, voila!  Cotton, ready to be picked.  Bolls in the field are likely to be much bigger and fluffier, but in the tightly controlled, windless atmosphere of a greenhouse chamber, this is what you get.

Here you can see flowers in many stages at once on a stand of plants in the greenhouse.

I took all these pictures today.  One plant will have flowers in all stages at once.  
Now of course the plant is producing flowers, squares, and open bolls all at the same time, being a perennial, and so if you simply ran a cultivator through the field you'd end up with a bale of cotton consisting mostly of leaves and dried flowers.  So once you have a good number of open bolls--and decades of breeding have produced , you have to spray a defoliant on the field to kill the plants and get the leaves to drop off.  It may be some weeks before you're ready to pull the cotton out of the field; those of you who've driven through the South around Thanksgiving time have seen the fields of cotton ready for harvest.  
I think the most interesting thing is the greenhouse chamber with all the flowering cotton plants has the most wonderful flowery scent.  Roses, which have no purpose other than to be pretty and smell nice, have been bred down to the point that none of the smell nice at all any more.  But here we have cotton, which nobody gives a rip about whether or not it smells pleasant and which has been bred for every reason but flower aroma, and they just smell fantastic.  We are a strange species, we humans.
Anyway, hope you've enjoyed this little photographic guide to the cotton lifecycle.  Now you how your T-shirt came to be.