In 1901, the Jewish National Fund was founded for the purpose of purchasing settlement land in Israel. JNF had the idea of placing a collection box in every Jewish home, and by the 1920s about one million of the famous "Blue Boxes" were in Jewish homes throughout the world. Besides purchasing land throughout Israel, JNF expanded into afforestation, water projects, agricultural innovation, roadworks, schools, and immigrant services. JNF operates under the principle that the Land of Israel belongs to the entire Jewish people; based on this, the Israeli Knesset later adopted a law stating that JNF lands cannot be sold, but only leased for periods of 49 years at a time. Over the past century, JNF has planted over 220 million trees throughout Israel -- the only nation in the world to end the 20th century with more trees than it had at the beginning.