277. Respirationlappears to be going on constantly, by day 

 and by night, during the Hfe of the plant, even wliile it is act- 

 ively engaged in the contravening process of the fixation 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 breatliing. .1 



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 wUl be found to contain 

 carbonic acid, rendering the Ume-water turbid. ' This effect will be produced, 

 whether the bell-glass stand in the sunsliine or in darkness, but the qiiantity of 

 acid evolved will be found to be much gi-eater in the darkness. \ 



279. Respiration is carried on with peculiar activity during 

 the two periods oil germination and flowering!) 



a. In gemaination/pure oxygen is absorbed, either from the air or water, or 

 both, in the absence of light (133, rf), and returned to the air combined with the 

 supei-fluous carbon of the starch, wliich thus is converted into sugar for the nour- 

 ishment of the young plant. ) 



h. It is also equally active ^t 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 ofi" 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, t ] 



280. The life of the plant depends upomihe continuance of respiration, for if it 

 be surrounded by an atmosphere with too great a proportion of carbonic acid, or 

 in a confined portion of air, which has become vitiated by its own action, and ex- 

 cluded from the light, its respiration is necessarily soon suspended, and it speedily 

 perishes. X\ 



f , 



281. Digestion, in plants, i consists properly of all those 



changes effected by the leaves in rendering the crude sap fit for 



the purposes of nutrition.^ But that process wMch is more par- 



* Carbonic acid is composed of 6 parts (by weigh!) of carbon, combined with 16 parts ol 

 oxygen. 



t Thus Saussure found that the flower of the Arum, while in bud, consumed 5 or 6 limes its 

 own volume of oxygen in 94 hours ; during the expansion of the flower, 30 times, and during 

 its withering, 5 times. When tlie floral envelopes were removed, he found that the quantity 

 of oxygen consumed by the stamens and pistils in 21 hours, was, in one instance, 132 times 

 Iheir own bulk. 



