LIMITING FACTORS TO GROWTH MEASUREMENTS. 333 



is limiting during the night that for the same culm the mini- 

 mum temperature would show some relation to the amount of 

 growth during the twelve hours of darkness. Plate 24 (below. 

 on right) gives the growth in cms. per 12 hours during the 

 night of Dendrocalamus at Hakgala from April 2nd to 3rd to 

 April 14th to 15th, together with the minimum temperatures 

 for the same period in F. c This period falls within that 

 portion of the Grand Period when the growth fluctuates about 

 a steady average value. 



The correspondence between these two curves is again 

 fairly close, though the measurements can only be roughly 

 approximate. It must also be stated that at a later period 

 in the growth of the same culm ne correspondence between 

 these two curves could be traced, so that little stress must be 

 laid upon this particular point. 



Consideration of all the facts of the Hakgala case seems to 

 niake clear that here, where the temperature is much lower 

 than any the species is exposed to in its natural habitat, the 

 temperature becomes the limiting factor of the growth when- 

 ever the supply of water to the growing culm is sufficient. 

 This is usually the case during the night, and may perhaps 

 occasionally be so during the day. As a rule, however, so much 

 water is drawn off to supply the transpiration of the adult 

 culms that the water supply during the day is not sufficient 

 even for the growth which would be permitted by the com- 

 paratively low temperatures recorded at Hakgala. 



4. Maximum Growth at the three places. 



Taking a general view of the growth at the three places it 

 has been noticed that the maximum growth recorded at the 

 three places for short periods of two hours is in proportion to the 

 temperatures recorded. These maximum growths are in 

 every case measured at a time when the water supply is either 

 sufficient or in excess (usually towards morning at Peradeniya 

 and Anuradhapura) , and therefore according to our view the 

 maximum amount of growth allowed by that temperature is 



