72 Keeble. — The Hanging Foliage of 
in a seedling Brownea grandiceps . The plant was raised in 
the diffuse light of a room, and when its leaves had assumed 
a good green colour it was placed in the open, exposed 
directly to the sun. The leaves acquired a distinct red tinge, 
so that probably, in response to the changed conditions 
of insolation, a new formation of coloured sap took place. 
Since writing the above I find in Johow’s paper already 
cited 1 the following statement, which seems to show to what 
an extent the amount of red colour in such leaves as these 
is the result of exposure to sun : ‘ That the appearance 
of red colour in the leaf is determined by light is shown 
by the fact that in cases where the different leaves are 
differently illuminated ’ (referring to Brownea and Acacia 
species) ‘ those leaves most exposed to the light possess an 
intense red colour, those more shaded a fainter red or even 
bright green.’ 
It was sought to determine by a simple experiment whether 
the coloured cell-sap had any noticeable influence in controlling 
the temperature of leaves exposed directly to tropical sun. 
For, although little is known as to the temperatures which 
leaves in exposed positions, as tree-tops, reach — such an in- 
vestigation being attended, as the writer found, by too great 
a personal equation on the part of the coolie employed in 
climbing the trees— it can hardly be doubted that at times 
the optimal temperatures for the various processes of the leaf 
may be exceeded. 
It was argued that if the red colour of such leaves as 
Amherstia nobilis has a protective value in mitigating the 
temperature within the leaf the fact might be demonstrated 
by the thermometer. 
The following experiment was made : 
First, red and green leaflets of Amherstia nobilis (the green 
being thicker and tougher) were laid side by side on the 
grass in the bright sun, and thermometers were placed on 
either set. 
1 Loc. cit., p. 300. 
