"When Iris came back she missed the pot of gold and of course she was in a sad way about it. She sent Mercury, the messenger of the gods, to look for it, for she didn't dare leave the rainbow again, lest somebody should run off with that too. Mercury asked all the trees if they had seen the pot of gold, and the elm, oak and pine pointed to the poplar and said,

"'The poplar can tell you where it is.'

"'How can I tell you where it is?' cried the poplar, and she held up all her branches in surprise, just as we hold up our hands--and down tumbled the pot of gold. The poplar was amazed and indignant, for she was a very honest tree. She stretched her boughs high above her head and declared that she would always hold them like that, so that nobody could hide stolen gold under them again. And she taught all the little poplars she knew to stand the same way, and that is why Lombardy poplars always do. But the aspen poplar leaves are always shaking, even on the very calmest day. And do you know why?"