1904] BERGEN—TRANSPIRATION OF EVERGREENS 289 
compass. It is this approximately vertical position of many leaves, 
with the silvery under surfaces facing in all directions, that gives the 
shimmering effect of olive foliage so often described. Figs. 7 and 8 
illustrate extreme cases of leaves standing vertically as above described.’ 
The thickness of sun leaves was in every case found to be greater 
than that of shade leaves, as 
described by Stanu and. others. 
In leaves of Quercus the ratio in 
thickness of the former to the 
latter was nearly 2.0; in Olea 
s> from 1.5 to 2.3; and in Pistacia 
y from'1.8 to 3-7. 
Ves In those species which are 
@ pubescent or scaly on the lower 
4 
surface the pubescence is much 
denser on sun leaves. It is gen- 
sie et, erally difficult to reduce the com- 
parison in this regard to a numerical basis, but an approximation of 
the kind can be made in the case of the leaves of Olea. The lower 
Surface of the leaf is always more or less completely covered with pel- 
late scales. On sun leaves the lower surface is so thickly scale-clad 
that the scales overlap considerably. 
Fic. 3.—Leaves of Pistacia Lentiscus: 
A, sun leaf; B, shade leaf. R54. 
found b bee 
’ Y measurements 
with the eyepiece micro- : 
iin Be ea on Fic. 4.—Leaves of Pistacia Lentiscus (another 
tree): A, sun leaf; B, shade leaf. Xo0.4. 
) The stomata were foy 
= than on shade ] 
9 Per cent. excess for 
nd to be somewhat more numerous on sun 
eaves; an average of two determinations gave 
the former. 
7 For these drawi ee : 
ngs the writer is indebted to Mrs. Herbert S. Jennings. 
