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maintained constant during the particular observation. In ﬁgure 63 is given records of rate of growth obtained with a specimen of Kysmn' at certain selected tempe'a- tures. It will be seen that the rate of growth increasos with the rise of temperature to an optimum, beyond which the growth-rate undergoes a wiepression. In the present case the optimum tempe'ature is in the neigh- bourhood of 35°C.

Fm. GIL—Effect of temperature on growth. and determination of optimum tem- pcraturc.

The method of observation that I have described above is not ideally perfect, but the best that could be devised under the circumstancs A very troublesome complication of pulsations in growth, arises at high temperatures, which render further record extremely «lilticult. Growth is un- doubtedly a pulsatory phenomenon; but under favourable circumstances these merge practically into a continuous average rate of elongation. At a high temperature the ell‘ect of certain disturbing factors comes into prominence. This may be due to some slight ﬂuctuation in the temperature of the chamber, or to the effect of thermal radiation from the side of the chamber. This disturbing inﬂuence is most noticed at about 45°C, rendering the record of growth above this point a matter of great uncertainty. It will