Fungous DiscAsrs of Plants, Pj-ach Yhllows 145 



crops for appropriating soil-nitrogen." The next year, Dr. G. C 

 Caldwell of Cornell University, reading a paper on "The Present 

 Aspects of the Question of the Direct Utility of the Free Nitrogen 

 of the Atmosphere for Plant-Food," ■*" reviewed the results of 

 study on the subject in England and continental Europe and said 

 of Halsted's paper: 



lliere appears to be no doubt that there is a close connection between 

 these tubercles and bacterial life. Hellriegel says they are filled with bac- 

 teria. Dr. Halsted, in his excellent paper on this subject, read at the 

 last meeting of this Society, says that there is no question but that they 

 become centres of development of bacteria in the soil and that there are, 

 moreover, motile bodies within their tissues which are probably bacteria; 

 but as to their function he suggests only a possible participation in the 

 ordinary nitrification in the soil. That there is anything more than this, 

 or that these tubercles have anything to do with the fixation of free nitro- 

 gen in connection with the growing legumes must as yet be regarded only 

 as an inference waiting for substantial proof. ''^ 



H. T. Pledge, in his recent book Science Since 1500,^' says that 



In 1866 certain nodules seen by Malpighi (1686) on the roots of 

 leguminous plants [had been] shown to contain bacteria. Ten years 

 later Berthelot took the subject up, and after a further decade showed 

 that certain bacteria present in the soil can fix nitrogen from the air. In 

 1887 it was shown that leguminous plants fertilise the soil by increasing 

 its nitrogen content, and in 1888 the Germans Helriegel and Wilfarth 

 showed that the bacteria in the nodules transform atmospheric nitrogen 

 into the nitrate form in which most plants take it up. 



Strictly speaking, these phenomena are not parasitic. 



The root-tubercle bacilli of the Leguminosae were believed, 

 during Smith's years of study, by some botanists to be parasites."*^ 

 His bibliography on the subject" included for the year 1888 also 

 a paper by M. W. Beijerinck entitled "Die Bakterien der Papi- 

 lionaceenknollchen," ^° and of this paper H. A. Harding, Ameri- 

 can plant pathologist, in 1912 said: '' "We have added little to 

 our knowledge of the histology of legume nodules since Beijer- 



*^ Proc. 9th Ann. Meet. Soc. Prom. Agric. Set. 21-24, 1888. 



*°Uem, 23-24. 



*'' Ministry' of Education, Science Museum, Philosophical Library, 256, 1947. 



*' Bacteria in relation to plant diseases, op. cit., 1: 64. 



Ide7n, 239-240. 



Botaitische Zeitung 46: coL 725-735, 741-750, 757-771, 781-790, 797-804, 1888. 



The trend of investigation in plant pathology, Phytopathology 2 (4): 161 f. 



49 



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