Sperm chemotaxis directions say to use 12-18 day old cultures. What exactly does this mean?

For sperm chemotaxis (e.g. Chemical Attraction – C-Fern Sperm Chemotaxis or simple observation) directions say to use 12-18 day old cultures. Does this mean I should sow the spores 12-18 days in advance, or does the 12-18 day age indicate the number of days after the gametophytes germinate?

The timing refers to the age of the cultures, day 0 being the day the C-Fern spores are sown (or the time spores first placed into water or are soaked). Under the recommended and standard conditions the spores germinate beginning at day 3 and subsequently gametophyte development will be quite rapid. At 28 °C and under constant light the gametophytes will be sexually mature by day 12 and sperm chemotaxis can be observed or tested any time from then until about day 18.

Be sure to keep in mind that when the C-Fern cultures are removed from warm culture conditions to room temperature, the sperm will release from the antheridia even in the apparent absence of liquid. All the supplies, equipment, and preparations should be made and organized before getting the cultures for observation or testing.