Tiny Tuesday - On the underside of a fern

I was fascinated on turning over a leaf on the fern I was watering, to see rows of tiny spores. It wasn't until they were enlarged on the screen that I could see they were not single spores, but actually clusters of many spores. 

There is obviously not a good strike rate or I would be living in a forest of ferns.

I have just worked out what they remind me of  - it is chocolate crackles - the chocolate/rice-bubble mix in cup cake papers, that children love.