100 THE LEAF, 
277. Respiration appears to be going on constantly, by day 
and by night, during the life of the plant, even while it is act- 
ively engaged in the contravening process of the fization of car- 
bon. ‘The result of it is, the removal of a certain superfluous 
portion of carbon, in a state of combination with oxygen,* from 
the nutritive substances of the plant, just as the same deleteri- 
ous acid is removed from the blood of animals by breathing. 
278. Let a few healthy plants be placed under a bell-glass containing air from 
which all the carbonic acid has been previously removed. After a few hours 
let the air be tested by shaking it with lime-water, and it will be found to contain 
carbonic acid, rendering the lime-water turbid. This effect will be produced, 
whether the bell-glass stand in the sunshine or in darkness, but the quantity of 
acid evolved will be found to be much greater in the darkness. 
279. Respiration is carried on with peculiar activity during 
the two periods of germination and flowering. 
a. In germination pure oxygen is absorbed, either from the air or water, or 
both, in the absence of light (133, d), and returned to the air combined with the 
superfluous carbon of the starch, which thus is converted into sugar for the nour- 
ishment of the young plant. 
b. It is also equally active at the time of flowering, a large quantity of oxygen 
being converted into carbonic acid by the flower. By this process it seems that 
the starch previously contained in the disk (107), or receptacle (59), is changed 
into saccharine matter for the nutrition of the pollen and ovules (70, 81), the 
superfluous portion flowing off in the form of honey. And it has been ascer- 
tained that the quantity of oxygen evolved bears a direct proportion to the devel- 
opment of the disk. { 
~ 
' 280. The life of the plant depends upon the continuance of respiration, for if it 
be surrounded by an atmosphere with too great a proportion of carbonie acid, or 
in a confined portion of air, which has become vitiated by its own action, and cz- 
cluded from the light, its respiration is necessarily soon suspended, and it speedily 
perishes. ¢ 
281. Diczsrion, in plants, consists properly of all those 
changes effected by the leaves in rendering the crude sap fit for 
the purposes of nutrition. But that process which is more par- 
* Carbonic acid is composed of 6 parts (by weight) of carbon, combined with 16 parts of 
oxygen. 
+ Thus Saussure found that the flower of the Arum, while in bud, consumed 5 or 6 times its 
own volume of oxygen in 24 hours ; during the expansion of the flower, 30 times, and during 
its withering, 5 times. When the floral envelopes were removed, he found that the quantity 
of oxygen consumed by the stamens and pistils in 24 hours, was, in one instance, 132 times 
their own bulk. : 
