LIMITING FACTORS TO GROWTH MEASUREMENTS. 317 



Table III. 



At Peradeniya. 



This, however, was not invariably the case (see Table III., 

 August 9 and 10). In the evening the temperature of the 

 culms was invariably higher than that of the air, often by a 

 considerable amount (see Table III., June 9th, 5.40 p.m.). 



These figures agree with the continuous observations every 

 two hours and show (1) the slower heating and cooling of the 

 culm so that the internal temperature lags behind the tem- 

 perature of the air ; and (2) the effect of exposure to sunlight, 

 which raises the general average of internal temperature, in 

 some cases producing a temperature higher than the maximum 

 experienced in the air. This general effect is seen in the 

 invariably higher temperature of the bamboo towards evening — 

 a difference which is often considerable if the day has been 

 sunny. 



Some such heating up must take place, and probably to a 

 more marked degree in Agave and Furcraea. These are 

 usually fully exposed to the sun, while the young bamboos 

 are often partly or wholly shaded by the adult members of the 

 clump. A rise of internal temperature when in full sun would 

 probably account for the rapid rate at which these grow under 

 such conditions. 



It being so clear that temperature is the factor which regu- 

 lates the rate of growth of these flowering shoots, we may 



