The rather odd-looking thing you can see below on the tip of a willow branch is called a pine-cone willow gall. It is caused by a gall midge, Rhabdophaga strobiloides. The midge deposits an egg in the developing terminal leaf buds of a willow branch in early spring. The larvae hatch, begin to feed and release a chemical which interferes with the leaf development of the willow, causing the formation of the gall, which looks a bit like a pine-cone. If all goes well, the adult midge emerges the following spring, after spending the winter developing in the gall.
Below you can see more of the tree, with several galls, from further back. Many other residents may also inhabit the gall. Some 31 potential residents have been identified, including beetles, caterpillars, sawflies, cynipid wasps, midges, spiders and the eggs of meadow grasshoppers. These other residents may cohabit peacefully with the gall midge, or they may eat it and take over its dwelling.
To view these galls, go south from the Bathurst St bridge, cross the small wooden bridge, and the tree with the galls is not far along at the next corner on the left hand side. I am thankful to Jessica Iraci of Parks for pointing out these galls to me and directing me to sources of information.
Turning to a totally different topic: there are many places in the ravine where you can see quite large patches of Joe-Pye weed. The one above is just one example of this colourful native flower. The ravine is at its summer best at present, so now is a good time to get out and enjoy it!