Here's what I did...
Started with my first search:
[ rotation flower stem ] – and found nothing.
Then, because I happened to know that plant movements like this are usually called "tropism" (which you could have figured out by using a reverse dictionary), I changed my query to:
[ rotation plan tropism ]
And deleted the "flower" term (as I thought it might be overly specialized). I found a pretty decent Google Books result. “Plant tropisms and other growth movements”
By skimming through that book, I learned the words “phototropism” and “heliotropism” (for movement towards light, and more specifically, movement towards the sun).
So that led me to read the Wikipedia article on heliotropism , which I got to my doing a serach for:
[ heliotropism ]
That was a pretty good article, which in turn led to me an article from the journal Natural History -- where learned that heliotropic plants can be much warmer than surrounding regions, giving insects a warm place to be and that the pulvinus is a plant organ for sun tracking - not quite what I need, but getting close.
But in reading this article from Natural History, I got the idea that what I was ACTUALLY looking for was not a tropism (which is a response to external stimuli), but something that's part of the natural growth pattern of the plant.
So now, I try the query:
[ plant stem spiral growth ]
After 4 queries and about 10 minutes of reading through articles, I've finally figured out the word that describes the situation at hand... that is, the rotational development of a plant stem as it grows outward.
While this is all great and good, I really really want to confirm that phyllotaxis is causing the mustard stem (and its flowers) to rotate as they grow.
And this is where I start to get stymied because I haven't yet found a convincing first-hand account of phyllotaxis in mustard plants (or a closely related plant, say another plant in the Brassica family).
Ideally what I want is a nice time lapse video, so I look for
[ time lapse phyllotaxis ]
And I find a JSTOR article “The origins of the spiral theory of phyllotaxis” William Montgomery -- looks interesting, but they want $38 for the article (arrgh! we call this a paywall, and it's deeply, deeply annoying).
I kept looking around for another hour or so, and learned that plants have circadian movements (day to night leaf folding) such as this video at Indiana University http://plantsinmotion.bio.indiana.edu/plantmotion/movements/leafmovements/clocks.html
- learned about nutational movements (light seeking… sunflowers waving around looking for light) and I learned about “nastic movements” – e.g., the shoot of a morning glory rotating to find a support (there is remarkable video footage here: http://plantsinmotion.bio.indiana.edu/plantmotion/movements/nastic/nastic.html - be sure to click on "morning glory twining")
A few images from their movie:
A few images from their movie:
SO... in the end, I've figured out what the term and concept describing this behavior is (phyllotaxis), but I have yet to find anything on the web that's specifically about the phyllotaxic movements of common mustard.
Looks like I'll have to take those pictures myself! Maybe a weekend project!!!