Statistical analysis—Temperature and growth correlation

The data obtained from the samples were analysed (Figs. 2-5) to determine if there were a relationship between temperature and three characteristic stem structures, namely, gonangia, terminal buds and axillary branches. Figure 2 expresses the relationship between temperature and gonangia. The Regression Curve equation page 7

Fig. 2 1967 autumn-winter seasons. Gonangia plotted against temperature using the statistical method of least squares.

Fig. 3 1967 autumn-winter seasons. Correlation between the average number of gonangia per stem, and temperature.

page 8 using the method of Heine (1966) is: Y = mX + c. The value of m = −0.45 and the value of c = 7.9. Therefore, Y = 7.9 − 0.45X. The correlation coefficient (r) for the gonangia is −0.94. Thus, the percentage of variability explained (r²) is 88%. Using a similar method, the percentage of variability explained for the terminal buds is 23% where Y = 121.28 − 5.56X, and for the branches 21.75% where Y = 83.62 − 4.73X. The same trend of increasing numbers of gongangia, etc., with decreasing temperature is seen using the simple graphic relationship for two variables (Figs. 3-5).

Remarks

Both series of statistical analyses demonstrate clearly that increasing numbers of gonangia, etc., are formed with decreasing temperature. Both series suggest (a) that in summer the production of gonangia, terminal buds and branches will fall to zero (Figs. 2-5), and (b) that temperature is a major factor in determining the trends of seasonal growth expressed by the erect stem (in terms of percentage of variability explained). Analysis by simple graphic relationship also demonstrates that great variation can occur in the percentage of stems possessing gonangia, terminal buds and branches within the weekly or monthly sampling period. Furthermore, this simple analysis suggests a critical temperature at which fluctuations in growth may take place. By critical temperature in this context, we mean that temperature above 13°C e.g., (Fig. 3) could either reduce or prohibit formation of gonangia or terminal buds. Temperatures above 11.5°C, e.g., (Fig 4) could either reduce or prohibit the formation of branches in the axil of the hydranth pedicel.

The annual range of morphology of the erect stem, described below, indicates however, that the relationship between stem growth and temperature is more complicated than is suggested by the results obtained from the autumn-winter seasons alone.