INTERNAL TEMPERATURE OF LEAVES. 273 



anthocyan tends to raise the internal temperature of the leaf. 

 Wliat biological advantage, if any, is gained by the plant in 

 this way is quite another question, but it is well to have this 

 physical effect definitely established. 



PART II. 



The second part of the paper will be occupied with an 

 account of some observations on the periodicity of growth of 

 certain trees at Peradeniya, and, as it suggests a theory which 

 may throw further light on the question of the biological 

 advantage of high internal leaf temperature, the final discus- 

 sion of that question will be reserved to the end of the paper. 



Periodicity Observations. 



Many of the evergreen trees of Ceylon, and also some trees 

 in Peradeniya Gardens which are not indigenous to the Island, 

 produce new growth during a very restricted period of the 

 year, and then rest from growth in length for a considerable 

 period. Observations were made of the frequency of this 

 growth period and the time of year when it occurred. In the 

 most typical cases the young foliage borne by the new shoots 

 is of different colour from the mature green leaves, usually 

 red or brown, occasionally white. The new growth is thus 

 sharply marked off from the old, and is at once noticed on a 

 casual inspection. In some cases the young foliage only 

 differed in being very much lighter green than the mature. It 

 was at first intended to make an inspection of the whole Garden 

 at Peradeniya once a month and note the names of the species 

 which were producing new growth. Owing to the fact that 

 the writer spent four months at Hakgala this could not be 

 carried out in full, but nine separate tours of the Gardens were 

 made extending over twelve months, and on each occasion a 

 record was made of all the species showing new growth at the 

 time. The table thus obtained shows to a certain extent the 

 frequency of this new growth and the months in which it is 

 most abvindant. 



A large number of the trees in the Gardens are not labelled, 

 and it was often necessary to bring in twigs and carefully com- 

 pare them with herbarium specimens before the species could 



