DISCOVERY OF THE LEGUMINOUS NODULES. 341 



The researches and calculations made by HELLRIEGEL (I.), in 

 particular, showed, however, that this addition of nitrogen is much 

 too small to deserve all the credit of the enrichment of the soil. 

 Moreover, since the supply is delivered in approximately regular 

 quantity to all the fields in a given district, it would afford no 

 explanation of the fact that, of all these fields (without nitrogenous 



s\v 



FIG. 60. Root-nodule of Vicia sativa. 



mw. main root ; sw. lateral root ; the meaning 

 of the other letters is given in Figs. 61 and 

 :F 63. Magn. 3. (After Seyerinck.) 



FIG. 59. Root of Vicia Faba. 



With young nodules on most of the 

 lateral roots and on the tap 

 root. Somewhat reduced. (After 

 Strasburger.) 



FIG. 61. Cross-section through a nodule of 

 Vicia sativa, cut along the line c in Fig. 60. 



pr. the primary integument with a few epi- 

 dermal bacteria (rb). 



xl. the vascular bundles, each with a xylem 

 fibre. 



bact. the strongly developed bacteroidal tissue. 

 Magn. 10. (After Beyerinck.) 



manure), it is only just those that have been planted with legu- 

 minous crops that yield such a surplus of nitrogenous matter. 



Consequently, only one other feasible explanation remains, 

 viz., that the Leguminosce possess the inherent property of absorb- 

 ing nitrogen from the air, and elaborating it into nitrogenous 

 compounds (albumin, &c.). 



However compulsory this conclusion may be, its recognition 

 by the majority of vegetable physiologists and agricultural chemists 



