A prisoner received a letter from his wife ：‘I have decided to plant some potato in the back garden。When is the best time to plant them？’The prisoner kmew that the prison police read all the letters，so he repliedin a letter：‘Dear wife whatever you do，DO NOT touch the back garden ！I hid all the gold there。’ A weekor later，he received another letter from his wife：‘You wouldn’t belive what happened。Some men came with shovels to the house，and dug up the whole back garden。’ The prisoner wrote another letter ：‘Dear， wife NOW is the besttime to plan the potato！’