The sperm of ferns detect unfertilized archegonia via a malate signal.

References

"In higher plants, we find positive chemotaxis in fern sperms, which respond to a malate signal from unfertilized archegonia." (Bar-Cohen 2006:474)

Book
Biomimetics: Biologically Inspired TechnologiesCRC/Taylor & FrancisFebruary 11, 2005
Yoseph Bar-Cohen