Page and Bod man 143 



it seems legitimate to conclude that a similar requirement might be 

 demonstrated in soil. Actually there is strong evidence for the essen- 

 tiality of oxygen for root development in either type of environment. 



Effect of soil aeration on root growth 



Much of the solution culture work has been done with tomatoes. 

 Arnon and Hoagland (j) obtained an average weight of 12.4 grams 

 per plant for roots in unaerated culture solutions as compared with 

 19.9 grams per plant for aerated solutions. The yield of tomatoes for 

 the aerated solution was 1.34 times that in the nonaerated solutions. 

 Arrington and Shive (4) obtained from culture solutions dry-weight 

 yields that were increased 210 per cent as the result of aeration. Erick- 

 son (34) too found that aerated plants were almost twice as large as 

 those which were not aerated. Clark and Shive (28) and Stiles and 

 Jorgensen (66) found that the dry weights of aerated roots were 1.6 

 times the weights of nonaerated roots, but Allison and Shive (2) found 

 this ratio to be only 1.12 for soybeans. Most workers have pointed out 

 that individual crops difTer in their oxygen requirements, but none pre- 

 sent clear-cut evidence that the roots of any plant can grow and func- 

 tion in the complete absence of oxygen. 



Gilbert and Shive (^5) give data for response to oxygen at various 

 levels for different plants, and Erickson (34) gives an excellent recent 

 review of the effects of oxygen in culture solutions. He found that root 

 growth increased in proportion to the oxygen content of the culture 

 medium. 



Several observations of rooting habits in aerated versus nonaerated 

 solutions are significant. Shive and his co-workers found that aerated 

 roots were long, slender, and much branched. Erickson observed root- 

 ing habits similar to those reported by Bryant (18) who found that the 

 length of aerated roots in his experiments averaged 37.4 cm., while 

 those of nonaerated plants averaged only 10.9 cm. in length. The non- 

 aerated roots were 15 per cent thicker than those aerated, and it was 

 observed that aerated roots had a longer portion of the root tip over 

 which absorption of water and salts could occur. 



Similar results have been reported for plants grown in soils. Loehwing 

 (48) found that soil aeration helped to produce plants having larger 



