112 



THE RATE OF GROWTH 



[CH. 



For an experiment on Lupinus albus, quoted by Asa Gray*, 

 I have worked out the corresponding coefficient, but a little more 

 carefully. Its value I find to be 1-16, or very nearly identical 

 with that we have just found for the maize ; and the correspondence 

 between the calculated curve and the actual observations is now 

 a close one. 



18 20 22 



24 26 28 

 Temperature 



30 



Fig. 26. 



Relation of rate of growth to temijerature in Maize, 

 values (after Koppen). and calculated curve. 



34°C. 



Observed 



Since the above paragraphs were wi'itten, 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 resultsy. 

 In Fig. 27 are shewn the mean rates of growth (based on about a hundred 

 experiments) at some thirty-four different temperatures between 0-8° and 

 29-3°, 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 1-092 per C.°, or 2-41 for an interval of 10°, and 

 a mean value for the whole series showing a rate of growth of just about 

 1 mm. per hotir at a temperature of 20°. 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 us altogether at very high 



* Botany, p. 387. 



t Leitch, I., Some Experiments on the Influence of Temperature on the Rate 

 of Growth in Pisum sativum, Ann. of Botany, xxx, pp. 25-46, 1916. (Cf. especiallj' 

 Table III, p. 45.) 



