and function, due to unequal illumination, than those leaves which 
flourish only for four or five months of the year. Broad-leaved ever 
greens, too, cast a denser shade than is afforded by ordinary conifers, 
and the leaves of the former therefore grow under more sharply con- 
trasting conditions than do those of the latter. 
The lack of suitable laboratory facilities has made it impossible 
for the writer to investigate the relative amounts of photosynthesis 
accomplished by the leaves of the species studied. It has been poss 
ble, however, to determine with a fair degree of accuracy the relative 
amount-of transpiration done by the sun leaves and the shade leaves 
of several species. 
The trees and shrubs mostly studied were: Olea europaea saliti, 
Pistacia Lentiscus, Quercus Ilex, and Rhamnus Alaternus. The obser 
vations, unless otherwise stated, were made upon leaves from thirteen 
to fifteen months old. Where sun leaves and shade leaves wert 
compared these were from different parts of the same shrub or {tee 
those which received only part of the total illumination being shaded 
wholly by their own foliage. 
s 
I. COMPARISONS OF COLOR, SIZE, SHAPE, AND STRUCTURE OF SUS 
LEAVES AND SHADE LEAVES. 
Out of ten trees and shrubs examined with reference to the effect 
of illumination on the color of the upper surface of the leaf, only one, 
Quercus Ilex, showed sun leaves always darker than the shade tt 
In this species the sun leaves when fully matured were gee 
to be of a very dark green, while shade leaves (1 to 2 per - 
nation) were of a grass-green color. ; 
- — Buxus dea ca no perceptible difference sacs 
to difference in illumination. ; 
Eight species (Arbutus Andrachne, A. Unedo, Citrus pet 
Myrtus communis tarentina, Nerium Oleander, Olea ee 
tacia Lentiscus, Rhamnus Alaternus) showed a much dar mes 
green in the shade leaves than in the sun leaves, though ae in 
shade leaves of Pistacia are lighter green. The shade lea per 
individuals studied received amounts varying from 1 we 
of the total illumination. d shade leave 
In comparing the relative areas of sun leaves 4™ 
