108 BACTERIA IN RELATION TO PLANT DISEASES. 



seem to me doubtful. I think he was experimenting with mixed cultures. Especially do I think his 

 theory of alternation of generations, in which Oospora is one stage, and an endospore bearing bacillus 

 another stage, not well supported. Possibly, therefore, the nitrogen stored in his flasks may have 

 been due to some other organism than Bad. leguminosarum. In no part of his paper are the details 

 of his experiments so stated that one could reproduce them. Apparently he did not make use of 

 poured plates, but depended for isolation on streak-cultures, made in tubes of slant gelatin. 



He states that the nodule-producing organism is pathogenic for some species of animals, e. g., 

 rabbits, but this also seems to me not well established by his experiments, since he obtained Oospora 

 and an almost round form of very small diameter from the rabbits inoculated with a supposed pure 

 culture of the nodule organism. Abscesses formed, locally, in the inoculated animals. 



In 1899, Maze published a fourth paper on the bacteria of leguminous root-nodules in which 

 he reviews the methods of Salfeld and of Nobbe for inoculating the soil with these bacteria, and in 

 addition gives some of his own experiences. 



Concerning Nobbe's work he says: 



To justify the method which he recommends, Nobbe starts out with the following hypotheses: 



There exist in the soil, neutral forms, capable of forming tubercles on the greater part of the 

 Leguminosae, and forms adapted to definite species. In general the infection of plants takes place 

 by the former, especially in uncultivated soil or in soil which has not borne Leguminosae in a long 

 time. The neutral form is modified profoundly by a passage through a leguminous plant becoming, 

 in this way, incapable of infecting other species. 



Bacteria thus adapted constitute a definite race : Thus the species Bacillus radicicola (Beyerinck) 

 or Rhyzobium pastcurianum (Laurent) comprises a certain number of races each possessing the ability 

 to infect particular species of Leguminosae. Sometimes a race is able to attach itself to different 

 plants, closely related botanically, but it is not able to utilize atmospheric nitrogen upon these 

 inappropriate hosts. 



Maze then raises the question, not mentioned by Nobbe, as to how these races pass over from 

 one season to another. He says : 



"May we conclude that they retain after months and years the ability of their ancestors to 

 live incapable of attaching themselves to plants of other species than the one which previously 

 sheltered them? Nothing would be less justifiable than such an assumption. It has long been 

 known in bacteriology, that all species of bacteria are subject to the influence of the medium on 

 which they live. More than any others, the bacteria of the Leguminosae possess this adaptability 

 which assures the dissemination and preservation of a species." 



Mazd claims that forms living in the soil lose, little by little, the characteristics which made 

 them easily identified when taken directly from the nodules. A dilution of soil applied to plants 

 growing in nutrient solutions caused nodules after 15 days. The same dilution inoculated on a series 

 of agar tubes, made for the purpose of obtaining isolated colonies, did not give any forms which 

 corresponded either morphologically or physiologically to the typical bacterium of the nodules. By 

 a long series of passages with all the species obtained from these cultures he states that finally two 

 forms were obtained which he identified by inoculations as the root-nodule organism. From this he 

 draws the conclusion that forms isolated from the soil acquire gradually, when subjected to a medium 

 containing the proper carbohydrate and nitrogen, the ability to elaborate the mucilaginous substance 

 and to fix atmospheric nitrogen. He thinks, therefore, that this ability is very unstable with the 

 bacteria of the Leguminosae. They acquire it in the nodules and lose it in the soil. 



He gives the following experiment as proof of this: 



He sowed the nodule bacteria on both sterilized and unsterilized soil kept saturated during 

 the whole experiment. On the unsterilized soil, conditions favored the growth of soil bacteria. 



At the end of 8 months it was impossible to obtain colonies resembling those which supplied the 

 bacteria sowed. On sterilized soil the bacteria removed from competition with other soil bacteria, 

 retained their initial characteristics after S months. 



He states also that the characteristics of these races of bacteria at the moment of isolation from 

 the nodules are far from being as distinct as Nobbe claims. Thus, for example, a bacterium coming 

 from one leguminous species is capable of attaching itself to certain other species. Nobbe admits 

 this but thinks that while able to form nodules the bacterium is no longer able on these strange 

 plants to fix nitrogen and so it becomes a parasite which is frequently injurious. 



Maz does not agree with this last statement: Bacteria from any of these plants will fix nitrogen 

 if they have sugar and enough initial nitrogen. The plants all offer that, and he says that the only 

 condition requisite to nitrogen fixation is their ability to penetrate them. This ability, he thinks, 

 depends on the alkalinity or acidity of the soil. He found that lupins inoculated with bacteria from 

 furze and broom formed just as many and as large nodules as those inoculated with bacteria from 

 the lupin, while the checks showed no trace of nodules. The furze and broom came from uncultivated 



