Other forms: anlagen
Use the biological term anlage when you talk about the very earliest, most basic form of a plant or animal organ.
An anlage is also known in science as a primordium. In either case, the word refers to an early developmental stage of an organ or tissue — an anlage is basically the potential for further growth and development, like an embryo that's brand new. You're most likely to encounter the word anlage in a biology textbook or article. It's a German word, meaning "foundation or basis," from the German verb anlagen, "to establish."