C-Fern: Root Tropism?

C-Fern: Root Tropism?
The Brief Story Behind the Question

Unlike animals, plants have limited power of movement and therefore respond to environmental stimuli in other ways. Major stimuli, such as gravity, light, and “touch” can produce a positive (towards) or negative (away from) response in plants by means of differential growth, in which different groups of cells increase or decrease their growth (elongation) in a way that reorients the plant part with respect to the direction of the stimulus. In C-Fern, sporophyte roots typically exhibit the standard positive gravitropic response. However, especially in dense cultures standard cultures grown under standard culture conditions (constant light and temperature) yield sexually mature gametophytes in about 2 weeks. If these cultures are watered once to effect fertilization a large population of synchronously developing sporophytes are produced. Over the next two weeks (primary) roots from these sporophytes elongate and begin to grow towards a “focal” point within the culture media.

C-Fern sporophytes – top of Petri dish (left
C-Fern sporophytes – bottom of same Petri dish (right). Note directional growth of roots towards a focal point in the center-left.

Your job is to explore, confirm, explain, or elaborate on this tropic response!

  • What is this tropism?
  • What other tropisms are evident in C-Fern?
  • Is this a repeatable phenomenon?
  • What conditions encourage/discourage this response?
  • What is the pattern of root development?
  • What is the origin and fate of the first C-Fern roots?
  • How do later roots arise?
  • Is there a good way to measure and quantify this response?
Thomas Warne