46 LEAVES 
Exp. 34, Class: Pour mercury into a “U” tube until 
it is about one-half full and then water until it is entirely 
full. Pass the cut end of a maple twig bearing about a 
dozen leaves thru a hole in a cork which fits the tube, 
so that it will project nearly I cm. into the water, Cover 
the cork with melted paraffin so that it will be air tight. 
After 24 hours measure the difference in the height of 
the mercury in the two arms of the tube and calculate 
the pressure. Conclusion? 
Exp. 35: Fasten two dry watch glasses to a large 
begonia leaf that is connected with a plant, so that one 
will have its concave surface against the upper surface 
of the leaf and the other its concave surface directly op- 
posite against the lower surface. The glasses may be 
held in place by means of a wooden test-tube holder, or 
small sticks held with rubber bands. After 24 hours do 
you find any moisture condensed on either watch glass? 
Strip a little epidermis from both surfaces of an old leaf. 
Dio you find stomata in both? Conclusions? 
Exp. 36, Class: Procure three leaves, two that have 
but comparatively few stomata (none on the upper sur- 
face) and a thick epidermis (e. g., oleander, begonia or 
India rubber) and one that has many stomata and a 
rather thin epidermis (iris or lily or any other plant that 
grows in a moist place). Cover the lower surface and 
the cut end of one of the two leaves with vaseline so as 
to close the stomata and hang the three leaves side by 
side. Which dries first? Conclusions? Strip a bit of 
lower and upper epidermis from leaves similar to those 
used and study it under the low and high power. Re- 
sults; conclusions? 
