BOOKS AND CURRENT LITERATURE 



Soil Aeration. — In a recent paper by Noyes, Trost and Yoder^ 

 variations in root growth under three sets of soil aeration conditions are 

 noted. The plants employed were Christmas pepper (Capsicum an- 

 nuum abhreviatum) , head lettuce (Lactuca saliva), radish (Raphanus 

 sativus) and green pod bean (Phaseolus vulgaris). These plants were 

 grown in Wagner pots, filled with Sioux silt loam in the case of Christmas 

 pepper and with Wabash sandy loam in the cases of the other plants. 

 All cultures were watered in a similar manner with distilled water. 

 One set of cultures was treated by flowing carbon dioxide continuously 

 in at the bottom of the pots at the approximate rate of 650 cc. per hour. 

 Another set of cultures received the carbon dioxide treatment eight 

 hours each day while a third set remained untreated. The roots of the 

 untreated Christmas peppers were large and fibrous while those treated 

 continuously with carbon dioxide were dwarfed, coarse and irregular. 

 The treated plants ^rmed many prominent aerial roots. The roots of 

 the plants receiving intermittent treatment were somewhat similar to 

 those receiving the continuous treatment. The aerial portions were 

 less affected although at first the growth of the treated plants was 

 somewhat retarded. The root system of the carbon dioxide treated 

 lettuce was affected to a much less extent than that of the Christmas 

 peppers. There was an indication, however, that the departure from 

 normal growth increased with the increase of carbon dioxide. The un- 

 treated radishes formed straight tap roots while those treated produced 

 large numbers of small horizontal roots from the base of the bulbs. 

 The response of the bean roots to the carbon dioxide treatments seemed 

 quite different from those of the other plants. These roots grew very 

 near to the openings where the gas entered and the intermittent treat- 

 ment seemed to produce the best root system. 



The results brought out in this paper substantiate those of some 

 other investigators in pointing out indirectly that the oxygen require- 

 ment in soils varies for different plants. Cannon and Free- observed 



1 Noyes, H. A., Trost, J. F., and Yoder, L., Root variations induced by carbon 

 dioxide gas additions to soil. Bot. Gaz. 66: 364-373. 1918. 



2 Cannon, W. A., and Free, E. E., The ecological significance of soil aeration. 

 Science n. s. 45: 178-180. 1917. 



215 



