circannuity

Looking at this almost dead bulb that stayed below ground for the whole year, I wondered whether I couldn't find a better use for the pot. It didn't look too pretty either in my living room, a pot with some mud, and some earth coloured thing sticking out. And as the guessing game about the real start of spring began (around March 2006 in S.Germany), lo and behold! This tiny mound sprouted green-stuff.

That set me thinking that I have heard of entraining in animals and plants due to light dark cycles. This allows our body to keep the 24hr day-night cycle alive (that is those of us who aren't sleep deprived and working on their computers at 02:01:02 hh:mm:ss).

It just so happened that the weekend following this amusing personal observation, I happened to be visiting the Landesmuseum Hessen in Darmstadt. The term circannual rhythms is used to describe the length-of-daylight time as an entraining mechanism for plants (seasonals) and animals (migratory birds). Some more interesting stuff I found here:
seasonality-blog.

What I still haven't understood however is:
1. When the bulbs of seasonal flowering plants are covered under the soil, they cant possibly be sensing the light. So what is it that entrains them? Is it temperature?

2. How accurate is this sensing? The "false spring" and its effect I have seen in Boston last year. It got far too warm for the season in the middle of winter, flowering started, and within a week it got miserably cold again and snowed shovelfuls. So the flowers seemed to have been to early. Maybe the plant can produce more. But what about a flock of birds and its decision to migrate hundreds of kilometres? What is the cost of that error? And how often does it happen? Are there correction mechanisms? How often does the time-of-the year detection fail?

If anybody knows the answers already, put in a comment please. Or a reference!

So now I will heed my own nighttime clock and shutdown.
Buenas noches.
c.