[lemma=by] □
[lemma=by] □ □
[lemma=by] □*
The best method of propagating most ferns is by division or by offsets as with Boston ferns . Furthermore existing lines of “ supportive stromal cells ” did not support expansion of HSCs ; at best they maintained the level of HSCs over time , presumably due to a steady state between generation of new HSCs by division and differentiation of “ old ” stem cells . Any organism that reproduces asexually ( for example , by division or budding ) may be considered immortal provided that its genome never changes .