408 SOILS: PROPERTIES AND MANAGEMENT 



demonstrated an oxidizing action of roots that is appar- 

 ently due to a peroxidase. Oxidation alone, however, 

 would hardly suffice to account for the solvent action 

 accompanying the development of plant roots, although 

 it is doubtless an important function and useful in other 

 ways. 



324. Importance of carbon dioxide as a solvent. — 

 Stoklasa and Ernst x have contributed much to this sub- 

 ject during the last decade. Stoklasa's earlier experiments, 

 conducted by maintaining the plant roots in a saturated 

 atmosphere, gave only carbon dioxide in the exudate. 

 In this he is in agreement with most of the recent inves- 

 tigators of this subject. Stoklasa emphasizes the im- 

 portance of carbon dioxide as a solvent by showing the 

 quantity produced by plants and by microorganisms. 

 He estimates that in one acre of soil to a depth of sixteen 

 inches there are sixty-eight pounds of carbon dioxide 

 produced by bacterial respiration in two hundred days, 

 and fifty-four pounds of carbon dioxide excreted by plant 

 roots in one hundred days; these periods he considers 

 as representing the year's activity of bacteria and higher 

 plants. 



In later experiments, Stoklasa and Ernst 2 found that 

 when plants do not have a sufficient supply of oxygen in 

 the air surrounding their roots, they secrete acetic and 

 formic acids from the root-hairs. These investigators 

 believe that these acids are toxic rather than beneficial, 



1 Stoklasa, J., and Ernst, A. Ueber den Ursprung die Menge 

 und die Bedeutnng des Kohlendioxvds im Boden. Centrlb. f. 

 Bakt., II, Band 14, Seite 723-736. *1905. 



2 Stoklasa, J., and Ernst, A. Beitrage zur Losung der Frage 

 der Chemischen Natur des Wurzelsekretes. Jahrb. f . Wiss. 

 Bot., Band 46, Seite 55-102. 1908-1909. 



