Classroom or Independent Research Using C-Fern – Large Data Sets, Qualitative and Quantitative Analyses

Several features make C-Fern ideal for individual or group experimentation and permit the rapid acquisition of very large data sets. Because C-Fern gametophytes are small, i.e. 0.5 – 3 mm at maturity, large populations consisting of 300 or more individuals can be cultured within small (60 x 15 mm) Petri dishes.

Many Petri dishes, totaling thousands of gametophytes, can be grown in a very small space, allowing for the participation of large numbers of students. Cultures of hundreds of gametophytes per Petri dish allow students to work with data generated from populations as well as individuals. In addition, the rapid development of gametophytes means that experiments can be repeated easily and that initial failure can be redone. These properties make it especially easy to generate extremely large data sets for individual and classroom level experimentation and thus provide an excellent foundation in sampling techniques and statistical treatment of data. The importance of an adequate sample size can be demonstrated in exercises using both class and individually acquired data. Meaningful descriptive and statistical analyses can be carried out easily.

Many developmental responses or events are easily quantified by counting or measuring using simple tools, e.g., grids, rulers, counters. For example, the percentage of germinated spores can be easily determined by counting the number of spores with protruding rhizoids relative to the total number of spores in a given sample. This initial discrete developmental stage can be used descriptively as well as to quantify the effect of external influences on gametophyte development; for example, the effect that temperature, chemicals, or light have on development. By assessing and graphing germination over time, students can gain insight into the description of a population response and developmental asynchrony.

Careful observation of C-Fern gametophyte development over time can serve as a prelude to more focused questions concerning the nature and origin of the two sexual types. Why are there two types? How do they arise? How are the frequencies of the two types regulated? What factors affect the frequencies of the two type? These and other student-generated hypotheses and questions can lead to experimental approaches addressed by collecting data on the percentage of sexual types under particular or defined environmental conditions. For example, what would be the sexual phenotype of an individual spore grown in isolation? What is the sex ratio within populations grown at different densities? Using these types of simple questions and others, students can derive and carry out a series of experiments that help explain fundamental developmental processes.

Because hermaphroditic gametophytes are morphologically simple, essentially two-dimensional, and develop from a localized notch meristem, their growth pattern is highly predictable and easily measured. Direct and meaningful estimates of growth can be based on linear measurements of gametophytes. Linear measurements correlate well with the gametophyte area and thus can be used to examine plant growth responses to any number of conditions or treatment variables.

Thomas Warne