Statistical analysis

Figure 6 shows the pattern of increasing numbers of gonangia, terminal buds and branches with decreasing temperature, but does not indicate the well defined seasonal growth forms indicated for the erect stem in the visually selected examples of the stem described above. Figure 6 also demonstrates that gonangia and terminal buds may occur throughout the year. However, in late spring (November) or in the summer months (December, January, February), the percentage of stems with page 9

Plate II

A: Tall, branched winter stems.

B and D: Short spring stems, with epiphytic diatoms.

C and E: Medium height spring stems.

F: Summer stems with epiphytic diatoms.

G and H: Autumn stems of O. geniculata. The epizooite is a species of Epistylus which is commonly attached to the erect stem at this season.

page 10 branches is very low. The percentage may even reach zero. Moreover, in the two late spring, summer seasons analysed, there is a well defined rise in the production of gonangia. This production rise of gonangia is more or less paralleled by increased numbers of medusae in the plankton.

Some of the data of the 1961-1963 collection series is shown statistically expressed using the method of least squares. The calculated percentage of variability explained for temperature and gonangia (Fig. 7) is 46.04%, where y = 3.06 — 0.15X. That is, at temperature 12°C, forty-six percent of the stems would have 1.2 gonangia per stem. For gonangia and branches (Fig. 8) the percentage of variability explained is 46.04% and Y = 0.15 — 7.63X. Also, the percentage of variability explained for temperature and branches and for temperature and feeding polyps was calculated, but is not figured. The percentage for temperature and branches is 27.5% and y = 0.176 — 0.0148X. In marked contrast is the percentage for the number of feeding hydranths on the hydrocaulus. The percentage explained is only 0.4% where y = 5.53 — 0.024X.