MYCODOMATIA OF THE ALDER, ETC. 



101 



provisionally distinguished as Frankia alni (Wor.) on alder, and 

 Frankia Brunchorstii (Moll.) on Myrica Gale. 



Hiltner,^ after a series of experiments, states that first-year 

 alders without tubercles do not thrive in soil free from nitrogen, 

 nor do they take up nitrogen from the atmosphere ; when, 

 however, provided with root-tubercles th,ey assimilate nitrogen. 

 The tubercles also functionate in water, and soU rich in nitrogen 

 has the affect of slightly increasing the assimilation of that 

 element. The tubercle-fungus is at first parasitic on the alder, 

 and is only of use to the plant after the tubercles have fully 

 developed. 



Mycodomatia of the Leguminosae. 



All Leguminosae growing in their native soils exhibit the 

 so-called tubercles. These are accessory formations of the 

 primary root-rind and are furnished with 

 vascular bundles, connected with the root- 

 bundles ; they consist of a cortex of normal 

 cells surrounding an inner large-celled 

 parenchyma with turbid cell-contents con- 

 sisting of numbers of bacteria, {Bacterium 

 radicola, Beyerink, or Bhizobium leguminos- 

 arum, Frank.) ^ 



Frank describes minutely the formation 

 of these tubercles.^ The short rod-shaped 

 microbe forces its way into a root-hair 

 or epidermal cell, multiplies there, and is 

 conducted to the inner cortical cells by 

 plasma-threads continuous through the 

 oell-walls. A rapid division of the inner 

 cortical cells is set up, till a tubercle is 

 formed, which may still further increase 

 by continued cell-division from a meristem p^ot.) 

 at its apex. The bacteria multiply simul- 

 taneously, and are transferred into the new cells where a 

 great change comes over most of them; they enlarge very 



' Hiltner, "Ueber d. Bedeutung d. Wurzelknbllchen v. Alnus glutinosa," 

 Ndbhe's Landwirtschaft. Versuchs-stationen, 1895. 



''Woronin, M^m. de I'acad. des sci. de St. Petersburg, 1886. 

 ' Lehrbuch d. Botanik, p. 271. 



Fig. 22. — RhizoJAum legum- 

 inosarum. Eoot-tubercles on 

 Genista tinctoria. (v. Tubeuf 



