RESPIRATION AND OXYGEN. 17 



after 8 to 12 days they completely lost their power of growth and 

 died for the most part, 



Arker (1901 : 431) investigated the influence of the surrounding 

 medium upon roots and showed that the rate of growth in roots of 

 Lupinus albus was increased when a stream of atmospheric air was 

 draw^n through the soil and when the soil-air was diluted to a certain 

 degree. The growth of roots of Lupinus and Helianthus in water 

 was faster when atmospheric air was bubbled through the solution. 

 The growth in mud was promoted by frequently renewing the water 

 and thus increasing the access of air. The retardation of root- 

 growth in water was less marked, since the oxygen is absorbed more 

 readily from water. The drawing of air through water does not 

 increase the oxygen-content, but keeps it nearer saturation. 



Strohmer (1903 : 933), in a comprehensive study of the respiration 

 of the sugar-beet, showed that some roots under normal conditions 

 excrete no other carbon-containing gas than CO 2. When wounded, 

 the sugar-beet showed an evident increase in the respiration inten- 

 sity. Ethyl alcohol was found to be a product of intramolecular 

 respiration. 



Newcombe (1902) observed that roots were distorted when grown 

 in closed tubes with water at 23° C. or above, and ascribed this 

 response to the possible absence of oxygen or the accumulation of 

 root secretions. 



Vochting (1902 : 87) studied the influence of aeration upon the 

 germination of potato tubers, chiefly by means of cylinders so ar- 

 ranged that the upper half would have well-aerated soil and the 

 lower half soil in which oxygen was more or less absent. In other 

 experiments, three layers of different air-content were arranged in 

 each cyUnder. In the case of cylinders of two layers, the upper pro- 

 duced many shoots and none or relatively few tubers, while in the 

 lower the results were just opposite. In the cyUnders with more 

 than two layers, the access of oxygen to the lowermost was so re- 

 duced that these decayed before further results could be obtained. 

 In the two upper layers the results were as indicated above. In 

 testing Stich's discovery that 3 to 4 per cent of oxygen did not mea- 

 surably decrease the amount of CO2 produced, tubers were placed in 

 an atmosphere of 4 per cent. After a few days sprouts appeared 

 and the amount of oxygen was then reduced to 3 per cent. Under 

 these conditions new sprouts still appeared and the oxygen was then 

 reduced to 2 per cent, where no further growth occurred. The shoots 

 apparently remained fresh and the experiment was continued for 

 4 weeks, when it was found that all tubers had decayed more or less. 

 He also found that the roots of potato tubers ceased to produce root- 

 hairs when the amount of oxygen was reduced to 3 per cent. In 

 experimenting with willow twigs, he showed that there was enough 

 oxygen in the water to maintain life, but not for the production 



