The squiggly lump on the stem is caused by aphids, that live inside the gall. The gall falls to the ground with the leaf in Autumn, and the aphids will overwinter inside, waiting to emerge in the Spring
Aphid gall on Poplar
Close up view of an aphid caused gall on poplar.
A4 photo print on a black background without a mount. Price includes standard UK postage - postings overseas will vary