688 



plants, and found that the formation of tubercles was very general in 

 this family. He found further, that there were bacteria associated with 

 all tubercles, and although the bacteria differed somewhat in the tuber- 

 cles of different species of plants, still there were certain constant char- 

 acteristics to be seen in them all. He therefore regarded the tubercles 

 as the result of the action of bacteria and gave to the organism 

 producing the tubercles the name of Bacillus radicicola. Beyerinck 

 regarded the so-called bacteroids of Woronin as degenerate forms of the 

 bacteria — involution forms, which appeared only after the bacteria had 

 lost their vigor. In a later investigation, after isolating the bacteria 

 and keeping them in pure cultures for many months, he was able to 

 produce the tubercles at will by inoculating soils in which his plants 

 were grown with the liure cultures of the organisms. 



In 1890 Prazmowski* published a detailed account of an extended 

 series of researches which he had been carrying on for several years. 

 He confirmed all of Heilriegel's results, showing conclusively that if 

 suflicient precautions were taken to sterilize the soil in which legumi- 

 nous plants were grown, no tubercles were ever produced; but that 

 they could be produced at will by the addition of soil infusion as above 

 described. He further showed that the tubercles grow in plants devel- 

 oping both in the light and in the dark, but are larger in plants 

 growing in the light; that they only appear in healthy plants; that 

 they are very few in plants growing in well-washed sand ; that if plants 

 growing in sterilized soil be watered with brook or river water, tuber- 

 cles occasionally develop, but never in abundance ; and that the infec- 

 tion of the roots occurs early in the germination of the plant and can not 

 take place in the older roots. All of these results indicated, of course, 

 that the tubercles were produced by certain micro-organisms which are 

 present in abundance in soils in which leguminous plants have grown, 

 but are not very abundant elsewhere. 



Turning to the study of the microscopic appearance, he found the 

 hyph.ie abundant in the young tubercles, and the bacteroids in the older 

 ones, as previous observers had done. Guided by the work of Beyer- 

 inck he found bacteria in abundance, and by causing them to grow 

 under the microscope thought he could verify the connection between 

 the bacteria and the bacteroids which had been described by Beyerinck. 

 Prazmowski then isolated the bacterium and made a careful study of 

 its characteristics. He prefers to call it Bacterium (instead of Bacillus) 

 radicicola, since it always appears as a short rod and never in the 

 f )rm of a slender thread. He found several varieties of the organism 

 associated with different species of leguminous plants. In all of his 

 artificial cultures the organism remained a typical bacterium, never 

 assuiuing the bacteroid forms which appear in the tubercles. From this 

 he concluded that the degeneration or involution forms appear only under 

 the influence of the root cells of the host plant. 



■ Laudw. Versuchs-Statioueu, 37, p. 161. 



