Last night I checked on my mango seed and found a thick, pale green sprout coming out of the seed's side. I planted the mango core on March 13 and did see one sprout a few weeks ago, which prompted me to take the seed out of the plastic bag in which I was hoping it would germinate and half-bury it in a planter filled with potting soil and dusted with a sphagnum peat mulch. Doing that seemed to cause the sprout to disappear rather than grow, so I thought I had killed it. The other day I examined the seed and it looked to be withering, like being buried in moist soil and peat moss for over a month had finally caused it to start rotting (There's no odor, mind you -- just a shrunken sort of look about the seed).
I was quite surprised when I found a sprout, although perhaps this semi-rotten state is precisely what is necessary to encourage germination. Either way, I'm just glad there's growth and I'm excited to see what happens next.
Here's a photo of the little sprout, taken by Steve with his Nikon D50: