262 FIXATION OF FREE NITROGEN BY BACTERIA 



in 1825. TJIEVIRANUS (I.), in 1853, was the first to regard these nodules as 

 normal growths, and thirteen years later they were studied by WOBOSIH (I.), who 

 made the (subsequently important) observation, that the formation contains 

 entirely closed cells filled with living bacteria. In the seventies ERIKSSON (I.) 

 and CORNU (I.) recognised these appendages as metamorphosed lateral roots of 

 perfectly unique structure. 



When regarded in section (Fig. 61), a nodule of this kind is seen at the first 

 glance to consist of two different portions a white or colourless external zone 



FIG. 60. Root-nodule of Vicia sativa. 

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

 the other letters is given in Figs. 61 aud 63. 

 Magn. 3. (After Jieyerinck.) 



FIG. 59. Root of Vicia Faba. 

 With young nodules on most of the lateral roots 

 and on the tap root. Somewhat reduced. 

 (After Strasburger.) 



cl 



FIG. 61. Cross-section through a nodule of Vicia 



saliva, cut along the line c in Fig. 60. 

 j)r. the primary integument with a few epidermal 



bacteria (rb). 



xl. the vascular bundles, each with a xylem fibre. 

 bact. thi; strongly developed bacteroidal tissue. 



Magu. 10. (After Jieyerinck.) 



and an interior layer, pale red in the young nodule, but afterwards greenish grey, 

 the line of demarcation between them being somewhat sharply denned, and the 

 outline indented like that of a blackberry. It is in the cells of this inner layer 

 that the bacteria now under consideration, and more fully described below, are 

 sheltered ; and the layer itself is known as the bacteroidal tissue. On account 

 of these enclosures the said root-nodules received from A. B. FRANK (III.) in 

 1879 the name of mycodomatia (i.e. fungus chambers), an expression that has, 

 however, been abandoned. 



193. Formation and Functions of the Nodules. 



The first to take under consideration the physiological importance of these 

 nodules was LACHMANN (I.), who in 1858 defined them as stores of albumen. 



