HOW THK PLANT M\KS 117 



2c. Oxygen 



19.'}. OxycT^^n is pssontial to all of tho lifo ]>ro- 

 cessos in tlu* {)lant, as wrll as to tlio animal. I*'or 

 j)orfoct pjerniinatioii oxyircn is rcMjuircd, and this 

 ^as (litTust'S into and is us«hI by all Iivin<; or «^rii\v- 

 iniT plant organs. The stoniata of Icavos and 

 slioots aro ineohanisnis insnriiiu: an ado()nat«^ 

 snpply for thfsc parts. P^iitrrniir these stoniata, 

 it is readily ditTused throui,di<»iit the ntMLrhhoriiiLr 

 ct'lls and tissues. 



1I»4. Oxyp:en is thru constantly " ahsoihcd," 

 and associated with this absorption is the givinj^ 

 otT of carbon tlioxid. This ai»])ropriation of 

 oxyL(<'n and escape of carbon dioxid are results 

 of respiration, a process equivalent in its ])ui'- 

 pose and results to respiration in animals. Vounir 

 pn^wini; ])]ants absorb an amount of oxyjj^cn about 

 equal to their volume, in from twenty-four t«> 

 thirty-six hoiu's. (fermimitinpf seeds absorb oxy- 

 gen, and give off ordinarily about an e(|ual (pian- 

 tity of carbon dioxid. 



1!).'). (lerminating seeds, opening flower bii<ls. 

 parts of plants that inive been injured, and cer- 

 tain organs in whicli decay is inuninent, resjure 

 more rapidly than other parts. Respiration prac- 

 tically represents molecular chang*' an<l the re- 

 lease of energy in the living substance. 



ion. Oxyir«n» is also taken in throuirh the 

 roots. Land plants, whose roots are deprived of 



