Sciency Answers: Another sticky question.

I got this question from Susan Sims:

What is that gummy, sticky film between the paper and the fruit on a tomatillo?

...and why is it there?

Eagerly awaiting a reply,

--Susan

My Sciency Answer:
It is all part of a scheme to make sure bugs don't eat the fruit, but birds do. Birds eating fruit is a good thing because then they fly around and poop the seeds out everywhere. But the birds can't eat it if the bugs get to it first. Tomatillos keep the insects away with a two-part defense system: Bad tasting chemicals, backed up by the sticky stuff Susan asked about.

The bad-tasting chemicals are called withanolides. The mature tomatillo makes lots of these in the little paper jacket (technically, the calyx) covering the fruit, but little of it in the fruit itself. Birds can pull off the gross husk and eat the yummy fruit, but insects just start eating, go "ick!" and fly away.
Which seems like a great system. So why does the tomatillo also make a layer of sticky? Because very small insects can slip in under the papery husk through an opening at the end. Very clever, these tiny little evil insects think themselves to be, but, before they can start to eat, they find themselves caught in the sticky layer and die. Bwahahaha!

So, to recap: Tomatillo protect their fruit from insects first with a foul-tasting papery covering, and then, just in case that defense is breached, they also make themselves into flypaper with sticky stuff, to keep their fruits pristine and perfect for hungry, seed pooping birds.

My explanation is primarily based on Chemical defence by withanolides during fruit development in Physalis peruviana by Baumann and Meier, so you can check out all the gory details there if you are so inclined.

Have a question? Send me and e-mail (engeizuki at gmail dot com) and I'll provide a sciency answer!

Another reason to mail order your bulbs?

I got a flower bulb catalog the other day from Colorblends. It was a bit late for me as I always put in my bulb orders back in June to take advantage of early-bird sales from my prefered source, McClure and Zimmerman, but I never turn down a chance to browse a catalog. One thing caught my eye: They had a little essay explaining that most daffodils sold in stores in the US are harvest and shipped too early, before they've had a chance to mature and dry properly, because big box stores demand early shipment to get their displays up early, and most independant garden centers feel forced to follow suit in order to compete. They say this makes the bulbs significantly more succeptable to fungal damage in shipment.

I always mail order my bulbs anyway (aside from a few impulse purchases) for the better selection and better prices. Guess you can add "not harvested too early" to that list as well.

Friday Cartoon: The bulb cycle