146 BOTANY 
Respiration is the oxidation of organic compounds 
to supply energy. Carbon dioxide is evolved. This 
can be shown to be most vigorous at germination and 
flowering, and can: be proved to take place in the green 
aérial parts as well as in the root. Compare with 
Photosynthesis. 
Transpiration is the giving out of the water 
absorbed by the root and transmitted through the 
vessels of the wood to the leaves. It takes place 
through the stomata of the leaves. It is more vigorous 
in the light, in a dry atmosphere, when it is windy, and 
when it is warm. The potometer measures the rate of 
transpiration. The control of transpiration is by the 
opening and closing of the stomata through the 
varying turgidity of the guard cells. 
Xerophytes guard against loss of water by thick- 
ened epidermis, leaf reduction, petioles forming 
phyllodes and twigs cladodes, and some by changing 
their leaves into spines. Fleshy stems conserve water 
in the plant, and creeping stems, rosette and cushion 
plants check evaporation from the soil. 
Protection.Scale leaves protect against drying 
out, hairs against heat and cold, and hair, spines, 
poison, and bad flavour against grazing animals. 
Water is prevented from adhering by glossy surfaces, 
hairs and gutter-like points. 
Shapes.—Ovate, obovate, cordate, obeordate, reni- 
form, peltate, hastate, sagittate, spatulate, lanceolate, 
oblanceolate, linear, and acicular. Reduction suits dry 
conditions. 
Veining is reticulate (pinnate and palmate) and 
parallel. Margins are entire, serrate, dentate, crenate. 
Pinnatifid, pinnatisect and pinnately compound leaves 
are derived from leaves pinnately veined. Palmatifid, 
palmatisect and palmately compound leaves are 
derived from leaves palmately veined. Division of the 
blade helps leaves to gather carbon dioxide and obtain 
