226 
PHARMACEUTICAL BOTANY 
throughout the entire plant and diffuses through the various 
cell-walls of cells, in contact with these, and passes into the 
interior of the cells. 
Here it oxidizes some of the carbohydrates 
breaking these down into carbon dioxide and watery vapor. 
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Fic. 155.—Demonstration of the 
liberation_of oxygen during photo- 
synthesis. A, release of bubbles of 
oxygen gas from the freshly cut end of 
the stem of Elodea in sunlight. B, 
collection of the gas, mainly oxygen, 
from Elodea in sunlight during photo- 
synthesis. If an aquatic plant be 
placed in a glass vessel of water under 
an inverted funnel over whose stem 
is suspended an inverted test tube 
filled with water, the gas given off 
by the plant will collect in the upper 
end of the tube and displace the water. 
Upon removing the tube and thrust- 
ing into it a glowing splinter, the 
latter will increase in brightness, indi- 
cating the presence of oxygen. (After 
Mottier.) 
These diffuse out of the cells into 
the intercellular-air-spaces and 
pass out of the plant through the 
same channels as oxygen entered. 
Respiration goes on both in light 
and darkness, organic compounds 
are broken down, O is absorbed 
and CO, set free, and potential 
energy is transformed into kinetic 
energy. The plant loses weight 
and, accordingly, this process is 
destructive in character. 
TRANSPIRATION is the action of 
giving off watery vapor. ‘The 
greater portion of the crude sap 
consisting very largely of water is 
conveyed upward as a transpiration 
stream through the trachee and 
tracheids of the roots and stems 
into those of the leaves. The 
latter pervade the soft, green leaf 
parenchyma and end in proximity 
to air spaces between the green 
cells. A portion of the crude 
sap diffuses into the leaf paren- 
chyma cells and is utilized in the 
nutritive processes such as photo- 
synthesis, digestion and assim- 
ilation occurring there. The 
remainder, which normally constitutes the larger part, passes 
through the intercellular-air-spaces and out of the leaves as 
watery vapor. 
About 90 per cent. of the water thus transpired 
escapes through the stomata, the remainder through the epi- 
dermal surface. It has been estimated that a large oak tree 
