THE ROOT-TUBERCLES OF BUR CLOVER (MED- 



ICAGO DENTICULATA WILLD.) AND OF 



SOME OTHER LEGUMINOUS PLANTS. 



BY GEORGE JAMES PEIRCE, 

 Associate Professor of Plant Physiology in the Leland Stanford Junior University. 



CONTENTS. 



Plate XXIX. 



Page. 

 I . Introduction and Method 295 



II. Origin and Morphology of Root-tubercles 298 



III. The Form and Distribution of Root-tubercles 312 



IV. The Structure of Root-tubercles 316 



Summary 324 



Bibliography 327 



Explanation of Plate 328 



L Introduction and Method. 



Some time ago, on casually examining some hand-sections 

 of the root-tubercles of Bur Clover {ATedicago denticulata 

 Willd.), I was struck by the great differences between the 

 cells containing bacteria or bacteroids and those in which 

 there were none. In these sections, the bacteria-containing 

 cells looked so unhealthy, as compared with the cells free 

 from bacteria, as plainly to suggest that the intimate rela- 

 tions of bacteria and leguminous cells were not mutually 

 advantageous, but that the bacteria were parasitic. There- 

 upon I began a careful microscopic study of the root- 

 tubercles of Bur Clover and other leguminous plants^ in 



1 Bur Clover was especially favorable for my work because, at most seasons, I could 

 get living plants from out of doors very near the laboratory, and I could grow such ma- 

 terial as I needed at other times from seed very quickly in the laboratory. Besides this, 

 however, I have studied Lupintis micranihus Dougl. var.^ir^j&r Watson, L. rivularis Dougl. 

 var. latifolius, Melilotus parviflora Desf., Medicago sativa J^inn., I/osaciia subpinnata Torr. and 

 Gray. The points which I wished to determine are essentially the same in all of these, 

 and hence my descriptions, though specifically of Bur Clover, are applicable to the 



others. 



[ 295 ] June 17, 1902. 



LIBRA 



