CONDITIONS AFFECTING LEGUME INOCULATION. 81 



forming bacteria is closely in acCord with field results reported by 

 various investigators, among whom perhaps Hopkins^' is best known 

 for his observations upon the cross-infection between sweet clover 

 and alfalfa and the absence of such cross-infection between many 

 other legumes. 



EFFECT OF AERATION. 



The aeration of soil for securing plentiful nodule formation is an 

 important if not a determining factor. The Ontario Agricultural 

 Experiment Station (Report for 1905, p. 39) reports a decided gain from 

 aeration in the case of a leguminous crop (peas) and no gain from the 

 aeration of a wheat crop. In the former case the result may be either 

 a direct one, affecting the activit}^ of the nodule bacteria, or it may be 

 that because of the abnormal growth of the host plant the bacteria are 

 unable to penetrate the root.* 



Our own experiments upon the effect of aeration are in accord with 

 those quoted in regard to the legumes, and the following is typical: A 

 light sandy soil, moderately limed, was used and the legume selected was 

 the garden pea. The aerated series was started in ordinary unglazed 

 1-inch pots, seedlings dipped in liquid culture when placed in position, 

 pots watered with a fine spraj^er, using tap water. The surface of the 

 soil was frequently stirred. The nonaerated series was made up of an 

 equal number (6) of glazed 4-inch pots with bottoms plugged with 

 paraffined cotton and the tops covered with paraffined paper to reduce 

 aeration. A separatory funnel (shown in PI. IX, fig. 1) was thrust into 

 each of these pots to admit water for growing the peas, and after inocu- 

 lating as with the other series the seedlings were introduced through 



« 111. Agr. Exp. Sta. Bui. 94, 1904, Nitrogen Bacteria and Legumes. 



& Livingston (Bot. Gaz., XLI, 2, 1906, p. 143; see also Bureau of Soils BuL No. 28) 

 reports a close relation between the growth of roots and tops in wheat, due to a dif- 

 ference of soil, which he explains as follows: "It would seem that the poor soil by- 

 inhibiting branch growth and causing the enlargement of cortical cells may render 

 the root system unable to carry on an adequate amount of absorption for normal 

 growth." If this effect upon the cortical cells should be found to hold true with the 

 legumes, it might have a direct bearing upon the ability of the bacteria to penetrate 

 and form nodules. The enlargement of the cortical cell is regarded as a phenomenon 

 of age, and it is reported (Maria Dawson, Phil. Trans. Eoy. Soc. London, Ser. B, 

 vol. 192 (1899), p. 24) that infection takes place most readily in quite young radicals. 



Aside from the effect of root development upon nodule formation, there is a pos- 

 sible interaction resulting in some way in greater root development where inoculation 

 takes place. In many cases which have come to notice where inoculated plants had 

 shown a superior development of the root system, it seemed at least justifiable to 

 regard the inoculation as assisting in providing the conditions favoring a healthy 

 root growth. In Bulletin No. 237 of the Cornell Agricultural Experiment Station, 

 page 165, it is noted that where no nodules occur the roots of alfalfa are simpler and 

 not so ramifying as where nodules occur. 



18270— No- 100—07 6 



