INTERNTAI- TEMPERATURE OF LEAVES. 293 



situations, and, taking a general view, it has been rightly 

 contended that on the whole the red colour' is abundant in 

 exposed situations, where presumably a screen from intense 

 light would be useful. The distribution would thus fit in with 

 the idea that anthocyan is a protective screen. When, how- 

 ever, it is shown from the habits of trees in Peradeniya that 

 even in what seem exposed sunny situations, the increase of 

 the transpiration stream may be an advantage ; it is at once 

 evident that tlxe argument against Stahl's explanation on the 

 ground of distribution becomes invalid. It may be tliat plants 

 in the open also find it an advantage for their transpiration 

 stream to be increased just as they do in those dark damp 

 forests , where live many of the plants cited by Stahl. In any 

 ease there is a big logical gap between the proposition " Antho- 

 cyan is distributed in such situations as make it possible for 

 it to be a light screen " and the proposition " Anthocyan does 

 act as a light screen." This gap does not up to the present 

 seem to be filled. In opposition to the view expressed m this 

 paper the cases may be cited of those trees, such as Humholdtia 

 lauri folia and Saraca indica, whose young foliage contains 

 very little anthocyan, and is almost white. These are shade 

 trees, as pointed out by Keeble, and it may be said that these 

 are the trees whose transpiration needs increasing the most, and 

 yet they liave not developed the red colour. In reply it may 

 be said that this paper has shown that the red colour of young 

 leaves leads to a higher internal temperature, and has suggested 

 that this higher temperature may have the incidental advan- 

 tage of promoting the transpiration stream, and thus of 

 rendering possible the development of the habit of general rapid 

 growth during a short period followed by a long rest. It is 

 no part of the purpose of this paper to show that the red colour 

 has always been developed in places where it would be 

 advantageous or that it has been most developed where it 

 would have been most advantageous. All that can be said 

 is that where it has been developed, it may be of advantage. 

 It might be incidentally noted that the trees coming under the 

 present writer's notice , whose young foliage is almost white , 

 are among those whose growth is not general over the whole 

 tree, but takes place nearly ail the year round in a few branches 



