I think I have solved the problem (or at least the problem as far as it occurs in my patch).
About 2 days before the jelly appeared, I found the remains of a dead frog in the same location. All that remained were a few scraps of skin, some parts of the digestive system and a ball of black egg nuclei (about 15 mm. diameter.) My deduction at that time was that a female frog had been killed and selectively scavenged. I did, however, wonder briefly where the jelly had gone. On revisiting the spot 2 days later, the frog bits had disappeared, but the jelly was there instead. (I should point out that it had been raining heavily during the interval. No surprise there.) My deduction was that this was indeed the jelly from the spawn, but where had it been hiding? If you consider that the volume of spawn laid by a single frog far exceeds the volume of a frog, we must deduce that the spawn expands after it is laid. This expansion takes place on or after exposure to the water that the spawn is laid in. I then thought about an egg-laying process that has become very familiar to me recently: the development of a hen's egg. The nucleus (yolk) is created first in the ovary and then passes through the oviduct where the jelly (albumen) is added as a coating. So at an early point in the process, the nucleus and the jelly are separate from each other inside the body of the frog. That must have been the point at which the frog was killed. The jelly was actually present when I saw the frog for the first time, but was minutely compressed and not visible. On exposure to the rain, the jelly expanded and became visible as the jelly lumps in the shot above. That's my theory, anyway.
No matter where I go, my camera is always with me: you never know when you'll get an opportunistic shot. Yesterday I visited a garden centre for a meeting and there were a few opportunities to look around and take a few shots. The weather was extremely variable with speeding clouds, occasional rain and some rare periods of sunshine. My radar went on to 'red alert' when a heavy shower was immediately followed by bright sun. I wandered over to where I had seen some mosses and saw that some of the capsules had indeed been soaked and there were a few with water droplets on them. This is the first shot:
|Funaria hygrometrica capsule with water droplet|
It's ok, but that horizontal brown seta in the middle of the shot is spoiling it. I knew the sun was very fleeting, so I had to act quickly. I pulled out the Swiss Army knife, opened the scissors and snipped off the offending seta, full in the knowledge that any excessive shaking could dislodge the water droplet (the brown seta was actually touching it). As soon as I took the following shot, the sun disappeared behind a cloud:
|Water droplet showing peristome teeth|
If you look closely, you can actually see the peristome teeth on the capsule (there are 16). These are used to open and close the spore capsule to allow or prevent the spores from being scattered, depending on humidity. Just for scale, the capsule is about 2 mm. across.