And corn belongs to the grass family, too, and corn is an Endogen, for it has a big pith instead of rings.
The Endogen flower is nearly always divided in threes, like the lily, which has six petals.
Will it be cleared of ambiguity by saying, "Every tree is endogen or exogen?"
Pipe-stems and fish-poles are hollow, but the cane we make them of is an Endogen, too.