296 RiVTTTri : 



5. An attempt was made to estimate the magnitude of the 

 cooling due to transpiration. Two leaves with stomata outwards 

 were consistently lower in temperature than two with their 

 stomatal surfaces facing each other. The difference was on an 

 average 2 • 5° C. 



6. Of factors tending to reduce the high temperature reached 

 in sunlight, the movement of the air is the most important. 

 Breezes of various strengths reduced the temperature attained 

 in sunlight by amounts varying from 2° C. to 10° C. 



7. A historical svirvey of the subject of anthocyan in leaves 

 is given, in which previous work is summarized as supporting either 

 (1) the t^creen theory of the function of anthocyan or (2), the 

 theory that anthocyan promotes transpiration and translocation 

 by raising the temperature of the leaf. 



8. It is shown experimentally — 



(a) That a red leaf attains a higher temperatxire than a 



white or pale leaf of the same thickness and texture. 



(b) That immature thin coloured leaves of various tropical 



trees may be either higher or lower in temperature 

 than mature thicker green leaves of the same species. 

 This probably depends on the amount of anthocyan 

 in the young leaf. 



Sfmmary (Pabt II.). 



9. Observations were made at intervals of the number of trees 

 showing new growth, the leaves of which were sharply marked off 

 in colour from the mature leaves. 



10. Analysis of the results showed that this new growth was 

 most prevalent in the driest season and almost absent in the 

 wettest months. This agi-ees with some observations on deciduous 

 trees at Peradeniya made by Wright (32). 



11. It is suggested that probably in a climate of high humidity, 

 like that at Peradeniya , it is only in the dry period that a sufficient 

 transpiration stream is obtained to supply the large amount of 

 mineral substances required in the formation of the copious new 

 growth. 



12. If this be rhe case, then the higher internal temperature 

 attained by the colouration of the young leaves would promote 

 the same object, viz., the increase of the transpii'ation stream. 



List of Literature. 



1. Askenasy. — Uber die Temperatur, welche Pfianzen im 

 Sonnenlieht amiehmeu. Bot. Zeitiing. 1875. 



2. Baumert. — Experimentelle Untersuch. uber Lichtschutze- 

 einrichtiingen an griinen Blattern, Beitrage zur Biologie der 

 Pfianzen. Breslan, 1907, pp. 86-161. 



3. Blackman and Matthcei.—A Ouantitatixe Study of Carbon - 

 dioxide Assimilation and T.eaf Temperature in Natural Illumina- 

 tion. Proc. Roy. iSoc, \ ol. B 76, 1905. 



