ELISHA MITCHELL SCIENTIFIC SOCIETY. 119 



within the j)eculiar structure of the tubercle dissolution of* their 

 bodies takes place, followed by an absorption of their protein 

 contents by the plant, so that not only nearly all of the substance 

 which the plant yielded to the parasitic organism is thus finally 

 restored, but in addition a tiiore costly element, atmospheric 

 nitrogen, which the organisms have assimilated and prepared 

 for their host. 



The chemical and physiological researches of Hellriegel and 

 Wilfarth,* Bertholletf and AtwaterJ show that the plants with 

 tubercles on their roots grown in a soil with very little nitrog- 

 enous substance gain more nitrogen than the soil contains, but 

 when grown in a sterilized soil no such gain is made. The experi- 

 mental researches of Prazmowski (loc. cit.) were directed to the 

 biological nature of the parasitic organism as well as to proving 

 that they were the specific cause of the tubercles. The plants 

 experimented with were peas, but he draws the inference that 

 the rest of the "Papilionaceen" are not essentially different in 

 the character of their tubercles. 



In brief, the results of his later researches§ are as follows : 

 The root-knots (Wurzelknollchen) of peas are not normal struct- 

 ures, for in sterilized media, protected from accidental infection, 

 they are never formed, but they always result from infection. 



The infecting knot-organisms are bacteria identical with them 

 in form and characters. The bacteria were taken from young 

 knots and increased throu2:h nianv i»:enerations by culture in 

 nutrient media. The causal connection between the bacteria thus 

 isolated and the root-knots was proven by a long series of careful 

 experiments wherein infection was produced through the inocu- 

 lation of cultivated plants with bacteria, originally taken directly 

 from the knots, and cultivated through many generations. The 



*Unter8uehungeti uber die Stickstoffnahrung der Gramineen nnd Leguminosen. 

 Beilagehaft z. d. Zeitsch. d. Ver. f. d. Rubenzaekei-Ind. d. D. R, Berlin, 1888. Abstract 

 in Bot. Centralblatt, Bd. XXXIX, pp. 138— 14^, 1889. 



tExperiences Nouvelles sur la fixation de I'azote par eertaines Terres vegetale et par 

 eertaines planter. Ann. de Chim. et de phys. G me. serie, T. XVI, Avril, 1889. 



JAtmospheric Nitrogen as Plant Food. Bull. No. 5, Storrs' School Exp. Sta. Conn., 

 Oct., 1889, 



gBerichte aus den Sitzungen der Iv. k. Akademie der Wissenschaften in Krakau, 

 Juni, 1889. 



Bot. Centralblatt, Bd. XXXIX, pp.356— 362, 1889. 



