290 BOTANICAL GAZETTE [october : 
In none of the species studied were any such extreme differences 
between the internal structure of sun leaves and shade leaves noted 
as have been described by STaut and others. Since the thickness 
and texture of the leaves of Pistacia differed more under different 
amounts of illumination than did those of any other species examined, 
special attention was paid to the 
histology of these leaves. The fol- 
lowing points of difference, many 
of which can be verified by refer- 
ence to figs. g-t1,® were made 
0 ‘ 
out: (1) cutinized layer of upper 
| epidermis much more developed 
in sun leaves; (2) palisade layer 
double in sun leaves and single in 
shade leaves, the cells next the 
epidermis longer in the former; 
(3) intercellular spaces smaller 1 
upper portions of mesophyll of 
: | d sun leaves; (4) bundles much more 
highly developed in sun Jeaves; 
5 (5) a palisade layer occasionally 
sun leaf, and B, shade leaf of Rham- developed next the lower epidermis 
nus; C,sun leaf, and D, shade leaf of 
Citrus. Xo.4. 
Fic. 5.—Leaves of Rhamnus 
in sun leaves. 
II. RELATIVE AMOUNT OF TRANSPIRATION OF SUN LEAVES AN 
SHADE LEAVES. a 
The three most obvious cases which present themselves for age 
gation are: (a) transpiration of both kinds of leaves, eee cht 
natural environment; (6) transpiration of both kinds 1n full s 
(c) transpiration of both kinds in shade. ch leaves 
No mode of determining the losses by transpiration ont f weigh 
‘as those in question is free from sources of error. Tee reven 
ing detached leaves, with the cut end of the petiole sealed ae for 
accidental loss, is an admirable one for succulent a sai use 
leaves with a less amount of stored water it is un so or Wel 
8 For these drawings the author is indebted to Dr. Grace B. Cooley 
College. 
