>produced a cluster of 'gemmae' - tiny green fragments that I
>guess will grow if I plant them separately.
You got it in one. If you look at each gemma, a handlens may
help, you will notice that one side has a small bump on it. This
is where the embryonic leaves and root will emerge. Place the
gemmae on the same media as the parents (I use 50:50 sand:peat)
with the bump facing UPWARDS and you will get many more plants
than if they are planted any old way.
Cheers
Terry