RESPIRATION AND OXYGEN. 25 



Free and Livingston (1915 : 60) have shown that cutting off the 

 supply of oxygen from the roots of Coleus stops absorption, and this 

 results in cessation of growth and wilting. When wilting did not go 

 too far, the plants could be revived by renewing the access of oxygen 

 to the soil. Cannon, and Cannon and Free, have carried out ex- 

 tensive investigations of root behavior under anaerobic conditions, 

 and their results are discussed in a later section. 



Butler (1919) has demonstrated that the sprouting of potatoes 

 was retarded by reducing the oxygen-supply or by lowering the tem- 

 perature to 3.7C., and that the former was more effective in this. 

 Respiration and consequent loss of weight were much influenced by 

 the humidity of the air. They were also rapid in wounded potatoes 

 during the first week of storage at 8 to 10 C. and then decreased. 



Rose (1915 : 435) determined that Martynia and Lactuca gave 

 germinations of 90 and 44 per cent respectively when treated with 

 80 per cent oxygen, but none when untreated. A 0.15 per cent solu- 

 tion of hydrogen peroxid increased the germination of Taraxacum 

 from 56 to 72 per cent and that of Datura wrightii from 20 to 100 

 per cent. 



Pember (1917 : 25) stated that aerating daily solutions in which 

 barley plants were growing did not noticeably change the growth 

 of the plants. This is explained, apparently, by the fact that the 

 solutions were changed every 2 weeks and water added at frequent 

 intervals to make up for water-loss. 



Fred and Haas (1919 : 631) have shown that the presence of soil 

 bacteria increases the etching power of the roots of Canada field peas. 

 This is ascribed to the normal CO 2 excretion from the living cells of 

 the root, together with carbonic and other acids evolved from the 

 dead or dying root-cells broken down by bacteria. 



Bergman (1920 : 13) has made a comprehensive study of the be- 

 havior of plants when their roots are submerged. When seedlings 

 of beans, balsam, and geranium in pots were submerged in bog-water 

 and tap-water until the top of the soil was covered, balsam began 

 to wilt in 2 days, was badly wilted in 3 days, and beyond recovery 

 in 4 days. The beans and geraniums began to wilt in 4 or 5 days and 

 at the end of 5 or 6 days the leaves turned yellow and dropped. 

 Under similar conditions Cyperus and Ranunculus grew vigorously. 

 In a later series, air or oxygen was supplied as soon as the plants 

 began to wilt, with the result that they regained their turgor, if 

 not too badly wilted, and grew normally as long as aeration was con- 

 tinued. In 8 to 10 days all the plants developed new roots at or 

 near the surface of the water, after which aeration was no longer 

 needed. Balsam plants aerated by bubbling air continuously 

 through the water in which they were submerged and by placing 

 Philotria and Spirogyra in it, wilted not at all or but slowly in con- 



