140 CLOVER CULTURE. 



epidermis beneath which are the root-bark cells ; in the cell t 

 the infecting- spore has entered ; in the bark cells lying- next 

 beneath, infection has also taken place, and they have thereby 

 become filled with a thick, shining- protoplasm, with enlarged 

 cell germs. This figure is magnified one hundred and 

 seventy-five times. Figure D is a more advanced stage of 

 the development ; / was the point of infection ; beneath, the 

 cells of first infection have by a process of cell-division, intro- 

 duced greater complexity and formed other infecting cells, 

 which are themselves upon the point of further sub-division \ 

 r, r is the root bark ; /z, /*, h rootlets ; en is the endodermis, 

 or inner skin within which lies the fibrous or woody part of 

 the root, not shown in the cut. This figure is magnified 

 seventy times. Figure E is a cross-section of a root with a 

 young tubercle. By means of a further increase of the 

 infected cells the bacterial tissue b has been formed, which at 

 02, m is in process of further development through division ; 

 / is the fibrous or woody cord of the root from which run 

 branches through the bacterial tissue ; r is the root bark. 

 The figure is only slightly magnified. Figure F is from 

 cells of the bacterial tissue, whose contents are clouded and 

 thickened by being filled with masses of bacteria. The cell 

 germs are visible and a few starch granules. The figure is 

 magnified 230 times. Figure G is a number, of bacteria 

 from the cells of F magnified 1090 times. Figure H\s> a 

 cluster of the Rhizobinum leguminosarum, produced by a 

 gelatine culture of the bacteria ; in the center is seen a few of 

 the latter within which clusters are visible. At s is seen 

 the cluster separated ; at z the zoogloa state composed of a 

 cluster that has united, 



At the same time that Prof. Helreigel and others were 

 prosecuting these investigations, Prof. W. O. Atwater, then 

 of Middletown, Connecticut, was performing the same 

 important service for America. In 1881 he instituted a 

 series of experiments which were repeated in 1882, and 

 brought positive evidence of the acquisition by peas of large 

 quantities of nitrogen from the air during their period of 

 growth. The investigation was unavoidably interrupted 

 until 1885, when four other series of investigations revealed 

 large losses of nitrogen during germination and early growth 

 in all cases where root tubercles were not formed. . The 

 results of the experiments of the first series were reported to 

 the American Association for the Advancement of Science 

 for 1881, and those of the first and second series together 

 were reported at the meeting of the British and 

 American Association for the Advancement of Science 



