I remember learning in my bio. class that since the oranges don't contain seeds, they cannot be cultivated normally. In order to be cultivated, a pipe is attached to a young citrus tree (a branch growing root, in this case) in order to connect the young orange tree to a full formed seedless orange tree. If the process of growth all goes well, the end result will be a tree w/ oranges without seeds ONLY since it was nurtured through a grown seedless orange tree.