294 BOTANICAL GAZETTE [ocroBER 
5. Shade leaves exposed for some hours to full sunshine may, 
without showing any signs of wilting, become almost unable to trans- 
pire. For example, a Q. J/ex shade leaf that during two hours in 
sunlight transpired almost one-fourth as much as a sun leaf from the 
Aono: 4Soam 
SULARAIRE UO 
Fic. 9.—Upper epidermis of Pistacia: A, sun leaf; B, shade leaf. X 230. 
same tree, was afterward in the shade found to transpire about one- 
sixtieth as much as the sun leaf in the shade. 
The fact that shade leaves transpire less than sun leaves, under 
similar conditions, may at first sight appear singular. But a little 
consideration will suffice to show that leaves of the former class are 
structurally unable to perform as much of any kind of work as are 
i PE rege ES a 
TIO DH O00GO¢ 
a 
. B, shade leal- 
Fic. 10.—Upper epidermis and mesophyll of Pistacia: A, sun leaf; B, sha 
Arak, 
the much 
opment 
stouter stems from which they spring, and the greater devel a : 
unit of time than shade leaves can. Also sun leaves, rs much 
ness two to four times that of shade leaves, usually ©o area 
of equal ft 
more interior evaporating surface than shade leaves 
