152 PHYSIOLOGICAL BOTANY. 



489. The results of both transpiration and respiration, as con- 

 cerns the plant, tend to concentrate the dilated sap by the elim- 

 ination of the water, which served merely for its conveyance, and 

 to assimilate it into food capable of being organized into cells 

 and their various contents. And it is proper in this place also 

 to notice the effects of this vast machinery upon the constitution 

 of the atmosphere and its relation to the animal kingdom. 



490. Carbonic acid gas is dissolved in the atmosphere and 

 somewhat uniformly diffused throughout its whole extent, in the 

 proportion of about 4 parts in 10,000, or -g^W This gas flows, 

 and is ever flowing into the air from decaying animal and vege- 

 table substances, from combustion, and from the breath of all 

 living animals. The quantity thus added to the atmosphere an- 

 nually is estimated at 100 billions Ibs., or nearly one-tenth of the 

 whole amount of carbon, and yet it does not accumulate. Now 

 if we were able to compute in pounds the annual growth of the 

 entire plant world, and the proportion of solid carbon which 

 enters into that amount, we should doubtless find that the grand 

 total of the demand equals this grand total supply. 



49J. And further: not only are the necessities of the plant 

 met by this wonderful circulation, but the necessities of animal 

 existence also. Carbonic acid is poisonous; and should it be left 

 to accumulate unchecked, it would gradually corrupt the air, and 

 within a few centuries extinguish all animal life. Thus are the 

 two kingdoms of the organic world mutually, through the inor- 

 ganic, dependent upon each other. The plant furnishes the 

 oxygen which the animal consumes, the animal the carbonic acid 

 which the plant consumes, while each would perish in an atmos- 

 phere of its own production. " Great and marvellous are thy 

 works, O Lord of Hosts ! in wisdom hast thou made them all." 



/fei'iew. 479. What is transpiration ? It occurs where and when ? 480. Why is absorp- 

 tion dependent upon it? What only does it expel? 481. How much water did a Sun- 

 flower transpire in a clay? A Cabbage? Effect of a forest on the Atmosphere ? 483. Im- 

 port of Aeration. Vastuess of the Apparatus. 484. Six fact* in Respiration. 485. The 

 two opposite phases of respiration. 486. When does the former phase become visible? 

 When the latter? Blanched plants. 487. Saussure's Experiments. Why no oxygen with 

 boiled water ? 489. The results of transpiration and respiration. 490. What proportion 

 or CO 2 in the Air? Whence is it? How much added yearly? Does it accumulate? 

 Why not * 491. How might the air become poison ? The" mutual dependence of Plants 

 tuid Animate. 



