An addition to the gall-ery

If you search for 'galls' in Blipfoto there are several pages of the things but I don't think this one is included.
Most galls on trees, bushes and plants are caused by tiny wasps, the plant tissue responding to their puncture by producing an eccentric growth in which the larva can feed and develop. This one is caused by a fungus, Taphrina pruni,  which infects blackthorn shrubs (and related plums and damsons too) in such a way as to take over the developing fruit and turn it into a swollen, distorted and infertile growth without a stone. The gall acts as a distribution point for the fungal spores which will infect other hosts. The stuff of nightmares and horror films!

On this twig you can see both the normal, small, round, green immature sloes and the brown, swollen fake fruit (sometimes called pocket plums because there is an empty space where the stone should be.) 

This gall is more prevalent in cold wet summers which is why there seems to be a lot of it about. Raining non-stop!