ID for tree gall please

[Dillybythesea]

Cotham Marble kindly steered me here, after I originally posted in Wildflowers, Plants and Trees. There's a tree in the hedgerow, willow-type, about 20' high, soft white pussy willows ahead of leaves, but covered in what I'm told are galls, probably bud galls (most are along the twigs but some are terminal). I took one home to investigate and you'll see that it had a nobbly outer layer, almost like seed-casings, set in a tough, corky layer, and inside this was a hollow space looking as though there had been several chambers. ID help would be much appreciated!

[Dillybythesea]

Having sent a specimen for dissection to an entomologist friend, Richard Dickson, I received this response:

> This one has no cavity. There is no frass (droppings), no silk, no shed skins - indeed I can say categorically that there has never been an invertebrate in it large enough to see without a microscope. The central core appears to be a thickened stem, and radiating out from this are what I believe to be distorted fruits of a female catkin.

Following up the suggestion of Andrew Halstead, I looked up the reference in the AIDGAP key to British Plant Galls. They write, "It is difficult to consider anything produced by a virus infection of plants as a gall, except possibly for the grossly distorted catkins of willows, Salix species (Fig. 3 Plate 8.2). This was originally thought to be due to a mite, Stenacis triradiatus.....but detailed anatomical studies by Wesphal & Michler demonstrated the presence of virus particles...." Elswhere he comments that these are "particularly prominent in winter". <