The Wisdom of Israel, by Edwin Collins, , at sacred-texts.com
A rabbi was passing through a field when he saw a very old man planting an oak-tree. He said to him: "Why are you planting that oak-tree, surely you do not expect to live long enough to see it grow up?"
"Ah," replied the old man, "if my ancestors had not planted trees we should not now enjoy their shade or their fruit. What my fathers did for me, that will I do for the future generations."