120 MAINE AGRICULTURAL EXPERIMENT STATION. 



ding, the irregular forms which have been called bacteroids. 

 The bacteroids are, therefore, not degenerate, but normal forms 

 of the bacteria. He further asserts that the bacteroids found in 

 the tissue of the tubercles arise by a normal process of budding 

 from the hyphae. The hyphae themselves he looks upon as 

 filamentous growths of the organism, and not as pouches filled 

 with bacteria nor as products of the root cells. Now, since bac- 

 teria always multiply by division and never by budding, it is 

 plain that if these observations of Laurent are correct, the 

 organisms in question cannot be called bacteria. Laurent, 

 therefore, like Ward and other earlier investigators, affirms that 

 the organism is really a low fungus, related to the yeasts in its 

 method of growth, and regards it as intermediate between the 

 yeasts and the filamentous fungi. He accepts the name form- 

 erly suggested by Frank, Rhizobhnn legutninosarum. 



The three views thus outlined give in substance our present 

 knowledge of the origin and structure of these tubercles. It 

 may seem strange that there should be such a difference of 

 opinion on mere matters of fact, but as indicated by Conn,* the 

 differences are explained by the difficulties of observation. The 

 tubercles grow naturally under ground, Laurent alone having 

 had much success with water culture. They are opaque, and 

 can therefore only be studied by tearing them to pieces or by 

 cutting sections of them. The only method of observation is 

 by examining a large number of tubercles in different stages of 

 growth, and in this way important points are sure to be missed. 

 Differences in results of observation as wide as above sketched 

 are. therefore, not surprising. 



Our present knowledge of the nature of these tubercles is 

 somewhat as follows :t "They are not normal products of the 

 plant, but are in all cases produced by infection from some 

 organisms which exist in the soil and attach themselves to the 

 young roots. Their presence in the tissue stimulates the root 

 cells to active growth and a mass of new tissue is formed around 

 the growing organisms. This tissue forms the tubercle and con- 

 fines the infectious action within narrow limits. The tubercle 

 is thus a sort of gall. The study of the development of this 



*Conn, 1. e. 

 fConn, I.e. 



