288 SMITH : 



the bamboo growth takes place in the season of highest humidity 

 during the south-west monsoon, w4iile the growth of the tree 

 occurs most abundantly during the period of lowest humidity. 

 It is in the demand for a large transpiration stream to bring 

 up the necessary minerals that a clue is perhaps to be found to 

 the close relation between dry weather and rapid growth in 

 these trees. May it not be that it is only in this drier period 

 that the humidity is low enough to promote the necessary 

 copious transpiration stream ? It must be remembered in 

 this connection how high a humidity prevails at Peradeniya 

 during some of the wetter months of the year. From July 4 

 at 10.40 P.M. to July 7 at 3.28 p.m. the humidity taken at 

 2-hour intervals did not at any time sink below 74 per cent, of 

 saturation, while even in the middle of the day very much 

 higher humidity than this was often registered. Thus, at 

 11.22 A.M., July 5, the humidity was 80 per cent., at 11 .25 a.m., 

 July 6, it was 91 percent., and at 11.18 a.m., July 7, it was 81 

 per cent. This occurred during a rather light south-west 

 monsoon. There is no doubt that in the usual monsoon 

 weather, all through June, July, and the greater part of 

 August at Peradeniya, the humidity rarely falls below 75 per 

 cent, and values of 80 per cent, to 90 per cent, in the day 

 are the rule, while 100 per cent, is often reached at night. 

 The same may be said generally of October and November, 

 the months of heaviest rain in the north-east monsoon, though 

 towards the end of November there is beginning to be a good 

 deal of sunshine in the morning. There are sometimes a few 

 days in November when rather dry winds cause the humidity to 

 fall, and records w^ere taken of humidity of 53 per cent, in the 

 middle of the day on November 3. Such days are not frequent, 

 as may be expected, considering the large rainfall of November 

 in normal years. In the dry period, beginning in December 

 and lasting through January, February, and March, there are 

 an increasing number of days in each month up to February, 

 on which the humidity of the air is low, and in February, 

 with the lowest rainfall of the whole year, there is an almost 

 continuous period of fairly low humidity. For example, on 

 February 4, 1907, the humidity was 57 per cent, at 10 a.m. and 

 at 11 A.M. had gone down to 48 per cent. 



