294 SMITH : 



at a time, thus making only a small demand upon the mineral 

 food supply at any one time. The causes of the developmeiit 

 of anthocyan in the young leaves of so many tropical plants 

 are not yet known. Investigation upon the lines of Overton's 

 paper seems most hopeful , and it is possible that a suggestion 

 of explanation on those lines can even now be put forward. 

 Owing to the absence of chlorophyll m the young leaf , the very 

 rapid growth which at first takes place must go on at the ex- 

 pense of material translocated from the stem, since the leaf 

 itself does not form food at all. It may be that the proportion 

 of sugar in the food thus being rapidly translocated into the 

 leaf is high, and that the young rapidly growing leaf contains 

 a higher proportion of sugar than the mature leaf does. If 

 so, according to Overton, the effect of light on a tissue richer 

 in sugars is to form anthocyan , and this would be only a special 

 case of a geneial law deduced by him from other instances. 

 When chlorophyll was developed in the mature leaf, and starch 

 thereby formed and accumulated during the day, the condition 

 of preponderance of sugar being absent, the anthocyan would 

 no longer be formed and the leaf would lose its red colour, 

 which is, of course, what actually does occur. 



It is possible that the sugars brought into the young 

 leaf, which are not products of its own activity may be 

 deposited as starch when they reach a certain amount. If so, 

 it may be that the young leaf is not richer in sugars than 

 the mature leaf , and some other explanation is to be looked 

 for. The question can only be settled by dii'ect chemical 

 investigation , which it is now impossible for the present writer, 

 who has left the tropics, to carry out. 



Wliat has here been shown is that by the absorption of radia- 

 tion the red leaf tends to have a higher internal temperature than 

 the leaf without anthocyan , that trees bearing such red leaves 

 have the habit of growing rapidly for a restricted period, and 

 that at Peradeniya this growth takes place j)rofusely at the 

 driest period of the year. It has been suggested that these facts 

 receive an explanation on the supposition that only at sucli 

 periods is tliere a possibility of sufficient transpiration to pro- 

 vide the necessary mineral foods for such ra])id growth. The 

 higher internal temperature of the young leaves caused b}' the 



