324 SMITH ■ wri.HATTOX of THE THEORY of 



Though not so obvious an effect as the one due to changes 

 of humidity (Lock) it is to be noted that the rate of growth 

 at the 6 a.m. reading on the nights in question was only about 

 two-thirds of the rate recorded at the 6 or 8 p.m. readings of 

 the previous evening, so that the falling off amounts to about 

 one-third of the fastest rate. It is so constant and so marked 

 as to be certainly outside the limits of error of the observa- 

 tions. No similar falling off in rate was observed either at 

 Peradeniya or Anuradhapura as is seen, not only by the curves 

 in Plato 24. but by those for each culm. 



5. Day Growth and, Humidity at Hakgala. 



The growth during the day at Hakgala is certainly controlled 

 by the humidity, as will be at once seen by the marked change 

 in growth from day to night and vice versa, and bj r a compa- 

 rison of the curves for humidity and growth during the day. 



Application of Theory of Limiting Factors. 



Such being the main results of the observations, it remains 

 to apply the theory of Limiting Factors and see if it furnishes 

 a general explanation of all the facts. 



Two Limiting Factors. 



Taking first the case of the bamboo at Hakgala, it will be 

 seen that unlike the case of Agave or Furcraea no single factor 

 of the physical environment controls throughout the 24 hours. 

 Obviously the humidity of the air is the governing factor 

 during the day. It will be noticed, however that at night the 

 humidity atands praotioally oonstanl at saturation 100% 

 and iliiis there is nothing in this factor to account for the 

 marked and steady falling oil' observed on so many occasions 

 The light is practically constant during the night, so that even 

 if the growth of the bamboo culms were affected by light, 

 u nioh Look | 1 2) denies, I Ins would not account for the steady 

 fall <>f growth rate. The factor which does decrease in inten- 



• v during the night ia 1 be temperature, and it will be observed 



