Jackie Gaff. (2005). I Wonder Why Pine Trees Have Needles: And Other Questions About Forests. Gardners Books.
Chicago-referens (17:e uppl.)Jackie Gaff. I Wonder Why Pine Trees Have Needles: And Other Questions About Forests. Gardners Books, 2005.
MLA-referens (9:e uppl.)Jackie Gaff. I Wonder Why Pine Trees Have Needles: And Other Questions About Forests. Gardners Books, 2005.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.