THE AERATION OF PLANTS 111 
tissues. A direct proof can be afforded by a simple experi- 
ment. If the lamina of a 
leaf is immersed in water, L 
air can be driven through 
it by subjecting the cut end 
of the petiole to gaseous 
pressure by means of an 
air-pump, or even by the 
effort of the lungs of the 
Fic. 79.—SEcTION oF A LENTICEL. 
observer, and can be seen 1, lenticel ; per, cork layer. 
to emerge from the surface 
of the leaf on which the stomatal apertures are situated. 
If a petiole is passed into a glass bottle through a tightly 
aes per. 
BoD 
Fic. 80.— APPARATUS TO SHOW CONTINUITY OF INTERCELLULAR 
Spaces In THE Luar. (After Detmer.) 
fitting cork, and covered with water, while the lamina 
remains in the air outside (fig. 80), bubbles of gas can be 
