IOWA ACADEMY OF SCIENCES. 



87 



researches made by Ward"*, Hellriegel ami Wilfarth"«. Laws and Gilbert"', 

 Beyerinck"\ Prazaiowski"», Liurent""*, Frank'=', Atkinson, and a host of others, 

 leaves no doubt as to the organisms found in the tubercles. 



The results of these later investigations show that in sterilized soil, leguminous 

 plants make but little growth and the tubercles will not develop. The results 

 have been further supplemented by the successful culture of the organisms by 

 Frank, Prazmowski, Laurent, Atkinson and others. There is much conflicting 

 testimony as to the true nature of the changes produced and the structure of the 

 organism. Atkinson says: "The important question is, can these various conflict- 

 ing notions of the biology of the microsymbiont be harmonized? Leaving out of 

 consideration for the present the real nature of the organism it will be admitted 

 by those who take the trouble to familiarize themselves with the scope of the work 

 covered by the most important investigations that the organism in question con- 

 sists of an elongated thread-like structure, which branches freely within the tuber- 

 cle and possesses enlarged portions which present a more or less finely lobed sur- 

 face; and very much smaller forms which must exist to some extent within the 

 tubercle, are capable of multiplying in artificial media, and when transplanted 

 from artificial media to the roots of leguminous plants, are capable under these 

 more natural conditions and the stimulus of the microsymbiont, of growing out 

 again into the threadlike structures." 



As to the place of the organism in the system of plants there is much diver- 

 sity of opinion. Laurent, as well as Ward, concluded that they were not bacteria 

 but low fungi. Atkinson says: "While in some characters, as noted above, the 

 tubercle organism is very much like Claodochj/trium tenue, yet in the sum of 

 essential characters it departs too widely from that genus, so that even if it should 

 eventually be clearly shown to be one ot the Chi/ti-idiacece, it would still be refera- 

 able to Phutottuixa.''' 



Frank, Prazmowski, and others placed it with bacteria. 



Whatever the final disposition will be, Atkinson, it seems to me, has good 

 grounds for calling it PJii/tomi/xa. 



It is not my purpose to discuss at length the chemical problem, but it may be 

 well to give the opinions of the more recent investigations. J. H. Gilbert^- says: 

 "The facts at command did not favor the idea that the plant was enabled to fix 

 this free nitrogen by its leaves. It seemed more consistent, both with experimental 

 results and with general ideas, to suppose that the nodule bacteria fixed free nitro- 

 gen within the plant, and that the higher plant absorbed the nitrogenous com- 

 pounds produced." Atwater and Woods "\ while they show that there is an acqui- 

 ts Ou the tubercular swellings on the roots of Vicia Faba. Phil. Trans. Koyal 

 Society, ULXXVIII (1887). pp. 139. 



116 Untersuchungen ueber die Stickstoffnahrung der Gramineen und Legumlnosen. 

 Beilageheft z. d. Zeitschr. f. d. Rubenzucker Ind. d. D. R. Berlin, Nov., 1888. Review 

 In Hot., Central b. XXXIX. (1889). ta8. 



ii"On the present question of the sources of the nitrogen of vegetation, etc. Phil. 

 Trans. Royal Society, CLXXX. B. 1-107. 



ii8Die Papilionaceenknoellchen, Bot. Zeit. 1888, p. 725-73.5, 741-750. 757-771, 780-790, 

 797-804. 



iiSDas Wesen und die blologische Bedeutung der Wurzelkncellchen der Erbse. Bot. 

 Central b. XXXIX. (1889). 3.56-362. 



i20Ann. d.rinstitut Pasteur. V. (1891). 105-139. 



i2iUeberdie Pilzsymbioie der Leguminoseen. Berlin, 1890. 



122 Experiment Station Record, Vol. Ill, p. 333. 



i23Atmospheric nitrogen as plant food. Bull. No. 5, Storr's School Agrl. E.\-p. Sta- 

 tion, Conn., Oct.. 1889. 



