108 THE VEGETABLE WORLD. 
would have risen to eight ten-thousandth parts. These experi- 
ments, in which there is an interchange of gas between the plant 
and the atmosphere, exhibit the double phenomena of absorption 
and exhalation in plants; in fact there is respiration. But the 
respiration of plants is not always the same, like that of animals, 
in which carbonic acid gas, water, and vapour is exhaled without 
cessation either by day or night. Plants possess two modes of 
respiration: one diurnal, in which the leaves absorb the carbonic 
acid of the air, decompose this gas, and extract the oxygen whilst 
the carbon remains in their tissues; the other nocturnal, and the 
reverse, in which the plant absorbs the oxygen and extracts the 
a yf een enter the mapota. ag — eit oat a oy f ths Gpechisee eg ane 
carbonic acid; that is to say, they breathe in the same manner 4s 
animals do. The carbon which is used by plants during the day is 
indispensable to the perfect development of their organs and the 
consolidation of their tissues. By respiration plants live and 
grow. 
It is necessary to remark here that it is only the green parts of 
vegetables which respire in the manner described; that is to 
say, by absorbing carbonic acid and disengaging oxygen under 
