70 AERATION AND AIR-CONTENT. 



Kosaroff (1897 : 604) in a study of the effect of temperature and 

 gases upon absorption, found that a lack of oxygen and the accumu- 

 lation of CO2 exerted an unfavorable influence upon the functions of 

 the plant. He was especially concerned to determine how far the 

 absence of oxygen was injurious and what part the presence of unde- 

 sirable gases played. He found that pure CO2 diminished both 

 absorption and transpiration. Plants whose roots were placed for 

 some time in an atmosphere rich in CO 2 soon lost their turgor, be- 

 came limp, and commonly died after further action. The injurious 

 effect of CO2 is its particular property, but it also emphasizes the 

 withdrawal of oxygen, and its influence upon absorption is, there- 

 fore, of a double nature. On the contrary, the depressing effect of 

 hydrogen operates only through the withdrawal of oxygen, and is 

 much weaker than that of CO2. Both gases also influence absorp- 

 tion unfavorably when the root is cut off. Pure CO2 affects the 

 transpiration of plants whose roots have been killed by scalding. 

 The author concluded that not only is the activity of the root 

 influenced by this gas, but it also enters the roots and probably 

 exerts an influence on the width of the stomatal opening, thus 

 further reducing the transpiration. In the case of seedlings, leafy 

 and leafless shoots and twigs (1900 : 138), carbon dioxid strongly 

 depressed absorption and hence transpiration, regardless of the part 

 used. It worked injury wherever it came into contact with living 

 cells. This was both a direct consequence of the action of CO2 

 and an indirect result of the exclusion of oxygen. The wilting of 

 plants with continued access of CO 2 was ascribed to the depression 

 of the transpiration stream. 



Livingston and Free (1917 : 183) found that absorption by the 

 roots of Coleus hlumei and Heliotropiuin peruvianum ceased within 

 24 hours after replacing the soil-air with nitrogen. Within 1 to 6 days 

 this was followed by loss of turgor in shoot and leaves, and finally 

 by wilting and death. In Nerium oleander, the disturbance of water- 

 relations in the shoot was indicated by the yellowing and loss of 

 leaves. Coleus recovered slowly with renewed access of oxygen, 

 while Heliotropium failed to do so after wilting became extensive. 

 The roots of the injured plants were found to be dead and partially 

 disintegrated. New roots were formed from the base of the stem in 

 Coleus on the readmission of oxygen. The injury due to the lack 

 of oxygen was found to be greatest with the plants possessing the 

 larger root-systems. The roots of Salix were found to function 

 normally in the absence of oxygen. 



Bergmann (1920 : 14) observed that geranium plants wilted in a 

 few days after the roots were subjected to carbon dioxid, the wilting 

 evidently beginning before all the oxygen was replaced. After 

 wilting, the leaves turned yellow and fell off to the end of the experi- 

 ment. Impatiens halsamina, under similar treatement, was slightly 



