LIMITING FACTORS TO GROWTH MEASUREMENTS. 323 



greater number of hours out of the 24 there. This gives us a 

 hint which will be developed later of the possibility of two 

 factors in the environment in turn controlling the growth of 

 the culms. What I wish to insist on now is the general fact 

 that, confining ourselves to growth for the short period of 2 hours, 

 the maximum rate of growth observed at the three places as 

 well as the general average of growth during the night, is 

 proportional to the temperature recorded, the lowest at 

 Hakgala, the highest at Anu radii apura. 



3. Comparison between Day and Night Growth at the 



three places. 



Hakgala is the only place where the rate of growth per 12 

 hours of daylight exceeds the rate of growth per 12 hours of 

 darkness. I have not myself observed either at Peradeniya 

 or Anuradhapura any case of the growth during the day being 

 greater than the growth during the night. Lock (12) during 

 a series of observations extending from June 19th to July 18th 

 on culms of Dendrocalamus only once recorded a greater 

 growth by day than by night at Peradeniya, 12*4 mm. per 

 hour and 12*2 mm. per hour respectively, the day in question 

 being one of continuous rain. At Hakgala, however, the daily 

 growth exceeded the night growth on nine occasions between 

 March 14th and May 5th, viz., on March 15th, 19th, 20th. 

 April 6th, 27th, 29th, 30th, May 1st, and 4th. 



4. Steady Fall of Growth Rate at Hakgala. 



The records of growth during the night at Hakgala show in 

 the majority of cases a steady falling off in rate. The curves 

 for the nights March 31st to April 1st and April 1st to 2nd, 

 are in this respect typical of a considerable number of obser- 

 vations made during the north-east monsoon. This decrease 

 in growth rate usually goes on steadily through the night, so 

 that either the 6 p.m. or more usually the 8 p.m. reading gives 

 the maximum rate for that night, all the later readings showing 

 a slower rate of growth. 



