curve and the actual observations is now a close one.
Since the above paragraphs were written, new data have come to hand. Miss I. Leitch has made careful observations of the rate of growth of rootlets of the Pea; and I have attempted a further analysis of her principal results62. In Fig. 27 are shewn the mean rates of growth (based on about a hundred experiments) at some thirty-four different temperatures between 0ôñ8ô¯ and 29ôñ3ô¯, each experiment lasting rather less than twenty-four hours. Working out the mean temperature coefficient for a great many combinations of these values, I obtain a value of 1ôñ092 per C.ô¯, or 2ôñ41 for an interval of 10ô¯, and a mean value for the whole series showing a rate of growth of just about 1 mm. per hour at a temperature of 20ô¯. My curve in Fig. 27 is drawn from these determinations; and it will be seen that, while it is by no means exact at the lower temperatures, and will of course fail