LIMITING FACTORS TO GROWTH MEASUREMENTS. 319 



Comparison of Absolute Bate of Growth at the different places. 

 As the temperature is the controlling factor in the growth 

 of the shoot, it would perhaps be expected that, setting aside 

 individual peculiarities of the plants measured, there would 

 be faster growth in the low country where higher temperatures 

 are the rule. Taking the total results of all the species, this 

 does not come out clearly, for, although the greatest growth 

 in two hours recorded in the whole series of experiments was 

 at Kandy, where the shade temperature reached 28° C, yet a 

 rate of 2 cms. per 2 hours was recorded at Hakgala with a 

 temperature of only 21 1° C, and this is considerably greater 

 than the growth at Peradeniya of 1 • 6 cms. per 2 hours with a 

 temperature of 29° C and the 14 cms. per 2 hours at Saha- 

 ranpur with a temperature of 30° C. It is in fact scarcely 

 to be expected that with different species and even genera at 

 different stages of growth any such uniformity should exist. 

 It is sufficiently remarkable that all show the same relation- 

 ship to one of the factors of the environment. It may be 

 pointed out, without much stress being laid on the fact, that 

 in the only case where the same species was measured both 

 up-country at Hakgala and at Peradeniya, the average rate 

 of growth as well as the maximum growth recorded was con- 

 siderably greater at Peradeniya, where the temperature was 

 higher throughout. The maximum growtli measured for 

 Agave americana at Hakgala was 1 • 1 cms. per 2 hours with 

 a temperature of 20*6° C, while the maximum growth of a 

 plant of the same species at Peradeniya was 1*6 cms. per 2 

 hours with a temperature of 29° C. 



• 



Summary for the genera Agave and Furcroea. 



It will be seen that the Theory of Limiting Factors is easily 

 applicable to the results for the cases so far considered. The 

 temperature of the growing shoot is the Limiting Factor 

 throughout, and we must suppose that both water and food 

 are available in excess of the requirements for any of these 

 temperatures. 



