38 Martin J. Prucha 



plants that had no nodules on their roots and placed them in a similar 

 solution to that used with the other plants, an immediate development 

 of nodules took place on the new rootlets. From this and other experi- 

 ments, Hiltner concluded that " the active nodules produce immunity 

 in the plant against the bacteria that possess the same or a lower degree 

 of infecting power than those already hving in the nodules of that plant. 

 Only bacteria of higher infecting power, are able to enter the root 

 tissue."*' 



Siichting (1904), believing that Hiltner's theory of the infecting power 

 of the organism and its relation to nodule development was not sound, 

 undertook a series of interesting experiments on this subject, as well 

 as an elaborate discussion of Hiltner's theory and of his o^vn theory. 

 In his experiments Siichting attempted to ascertain three points: (1) Have 

 the organisms that produce the first nodules on the plant less infecting 

 power than those that produce nodules on the same plant subsequently? 

 (2) Does the symbiosis with the plant influence the infecting power of 

 the organism? (3) Does the artificial medium influence the infectii?g 

 power of the organism? 



From his experiments Siichting drew the following conclusions: 



1. The infecting power of the bacteria is not proportional to the age of 

 the nodule. 



2. The passage of the bacteria through the host plant does increase 

 their infecting povv-er. Their infecting power does not vary at the different 

 stages of the plant's vegetative period, and the feeding of the plant by 

 potassium nitrate is injurious to the bacteria in the nodules. 



3. When propagated on artificial media the lupine bacteria lose their 

 infecting power on some media and may exist in a so-called pseudo form. 

 On neutral media the bacteria retain their infecting power better than on 

 acid media. The horse-bean bacteria do not behave in the same manner, 

 but keep their infecting power for a long time on suitable media. 



Lewis and Nicholson (1905), on the other hand, found by their experi- 

 ments that " It seems that the presence or absence of nitrogen in the 

 culture media is not the determining factor in maintaining the activity 

 of the germ. Cultivation in the presence of the amount of nitrogen 

 usually present in bouillon with from two to five per cent of cane sugar 



6 Translation from ths original German. 



