FUNCTIONS OF LEAVES 1338 
surfaces. Stomata occur on the epidermis of young stems, 
being replaced later by the lenticels. Those plants which, 
like the cactuses, have no ordinary leaves, transpire through 
the stomata scattered over their general surfaces. 
EXPERIMENT XV 
_ Amount of Water lost by Transpiration. — Procure a thrifty hydran- 
gea! growing in a small flower-pot. Calculate the area of the leaf- 
surface by dividing the surface of a piece of tracing cloth into a series 
of squares one-half inch on a side, 
holding an average leaf against this, 
and counting the number of squares 
and parts of squares covered by the 
leaf. This area multiplied by the 
number of leaves will give approxi- 
mately the total evaporating surface. 
Transfer the plant to a glass bat- 
tery jar of suitable size. Cover the 
jar with a piece of sheet lead, slit to 
admit the stem of the plant, invert 
the jar, and seal the lead to the 
glass with a hot mixture of beeswax 
and resin. Seal up the slit and the 
opening about the stem with graft- 
ing wax. A thistle-tube, such as is 
used by chemists, is also to be in- 
serted, as shown in Fig. 95.2 The 
mouth of this should be kept corked 
when the tube is not in use for 
watering. 
: Fig. 95. A Hydrangea 
1The common species of the green- for Exp. XV. 
houses, Hydrangea Hortensia. : 
21t will be much more convenient to tie the hydrangea if one has been 
chosen that has but a single main stem. Instead of the hydrangea the com- 
mon cineraria, Senecio cruentus, does very well. 
