Seed production vs. Bulb size

Any of you that may lurk on the Rock and Alpine Forum may remember me posting about the Scottish plantsman Ian Young. He has proven that allowing seeds to develop on many different bulbous plant species (that normally go dormant during the hot summer) does not reduce bulb growth for that season. In fact, often an increases of bulb size is observed, compared to plants whose waining flowers were removed.

He observed that these bulbous species , stay green and actively growing later into the summer if they produce seed, compared to plants of the same species that do not have seed pods. He theorizes that because the plant is actively growing longer, it has a longer time to replenish the bulb, thus producing a large bulb.

While he has not tested any Lilium species (as far as I know), he has proven his hypothesis with several summer dormant Fritillaria species, and from Fritillaria to Lilium is not a huge jump. And similarly, while the Lilium genus does not normally go dormant for the summer, there are times when plants will shut down prematurely due to various stresses.

Fear not, all this drivel does have a meaningful end.

Look, Look! (at the pic) My own unintended "experiment" supports (so far) this same theory. Five plants of Lilium amabile bloomed with two or three flowers each. (The small stems are from stem bulblets from last year.) Two were allowed to set seed, the others had their flowers removed once they withered. The three without seedpods are turning yellow and going dormant, while the two with seedpods are still healthy green. Hmmm . . .

I will be planting all these this fall in the garden, and then I will see which bulbs are larger . . .

Rick

Will look forward to more of your observations.

Interesting. Seems to fly in the face of logic. Creating seed pods should expend the plant energy, not invigorate it. Waiting to see more.

When you say it like that it sounds logical. Have seen the same on some of my own lilies that those that have seedpod stay green longer.
Thanks for informing.

The Results

Firstly, I have to say this isn't a fair experiment, because my growing season was barely long enough to produce seed naturally. Pods cracked open while leaves were still green, but were already senescing. Non seed producing stems had turned brown only about 2 weeks before. This year has been unseasonably cool. Perhaps a normal Minnesota season with more heat would have be more adequate for believable results.

Pictured below are the findings from 18 Oct. The two on the right, still with stems (leaves had completely withered), are the ones that produced seed. On the left are the two where I remove flowers when they withered. I would label this test inconclusive, because of the aforementioned caveat, even though the two seed producing bulbs are a bit smaller.

Although all were originally planted the same, what I did find interesting was the corresponding depth in the soil where I found each bulb to be now. The photo is accurate in this respect. The two non seed producing bulbs were deeper by the amount shown. At first I found this to be a curious phenomenon, but after giving it some thought, it is exactly what I would expect at these stages of growth. (That's a clue.)

Your homework is to figure out why the bulbs grew at two different depths, and explain it to the rest of us.

Papers are due by Monday.
Class dismissed.

Well, let's see.... I'll probably miss class tomorrow due to hangover (big football weekend, you know) So I'll shall now submit my 'Cliff's Notes' amount of thought I've managed to muster:

Perhaps the lilies that there unable to seed (due to human intervention) hunkered down to allow the stem bulblets a fighting chance. Having taken away one mode of reproduction caused the other to become enhanced.

Gee, hope I don't get sent to the principal's office.

Since I received only one paper (a valiant effort, but still incorrect), perhaps another clue:

Contractile roots, that pull the bulb deeper in the soil, are not muscles. They are not comparable to the human anatomy. They work by dying.

Let me explain. Notice that a contractile root will have roots branching mainly at the end of the main root, rather than all along its length. Where the root branches is the anchoring part that will provide a hold fast by which the bulb is pulled down. But how does the root actually pull down? Herein lies clue #2: the root must die. As the root dies and dries, it shrinks, becomes shorter, and pulls the bulb lower. Contractile roots, therefore, are ephemeral by definition. If they were long lived, they could not be contracting roots.

The essay due date has been extended until Saturday.
Class dismissed, again.

Well, a bunch of lackadaisical hohums here, I see. Or you're so something from Thanksgiving that [enter lame excuse here].

Sigh . . .
= = = = = = = = = = = = = = =

Kidding. I'm Kidding!

Answer #1
The contractile roots have not died and dried enough to pull down the two bulbs on the right. (Notice the stems are still green.) Since the bulbs on the left had gone dormant earlier, their contractile roots have already dried and done their job.

Answer #2
As I continued to ruminate on the matter, I came up with another possible reason. I wouldn't expect anyone to know this, but apparently it takes a lot of energy to produce contractile roots. Perhaps the two rightmost plants expended their energy on seed production, instead of contractile root construction, and so had nothing to pull themselves down with.

Seems reasonable, but makes my brain hurt. :)