ROLE OF THE NODULE BACTERIA 463 



support certain species of beans, peas, or clovers producing a large 

 crop, developing quantities of tubercles and fixing an abundance of 

 nitrogen, while the same soil will not support other species of legumes 

 with equal readiness. ... It certainly means that different 

 species of legumes demand different varieties of tubercle bacteria. 

 Whether these different varieties are distinct species is, of course, 

 a fruitless question, inasmuch as we do not know what we mean 

 by a species among bacteria. But it is of importance to know whether 

 these types are quite distinct or whether they are simply physiological 

 varieties of the same general species. If the former is true we should 

 expect them to remain distinct, but if the latter is true, we might 

 expect the soil bacteria to be capable of adaptation by cultivation 

 to different legumes. On the whole, the evidence is decidedly in 

 favor of the latter view and indicates that the different tubercle 

 bacteria are probably all one general species, but that under different 

 conditions they assume slightly different physiological relations. 

 They can accommodate themselves to grow in one or another legume, 

 and having become especially adapted for one species, but allowed 

 to develop in the soil in which the latter plants are growing, they 

 will adapt themselves in time to the new plant. In other words, 

 experiments indicate that there is probably one species of tubercle 

 bacteria, and that this species assumes different physiological char- 

 acters under the influence of the different conditions in which it 

 grows." 



The Bacillus or Bacterium radicicola, according to Prazmowski, 

 penetrates into the epidermis cells of the root hairs of leguminosse 

 and develops a colony which surrounds itself with a tough membrane. 

 From the point of entrance a sac filled with bacteria is then formed. 

 It grows toward the cortical cells and penetrates into the interior of 

 the root hair, where it stimulates the cells to proliferation. The sacs, 

 also called the infectious filaments, are not part of the leguminous 

 plant, but are derived from the gelatinous (zoogleal) substance of 

 the bacteria. The different parts which constitute the infected 

 cells can be demonstrated by a mixed watery solution of fuchsin 

 and gentian violet in 1 per cent, acetic acid. Sections of the nodules 

 or tubercles stained with this solution show the plasmatic contents 

 and the membrane of the leguminosa cells blue, the bacteria red, 

 and their common zoogleal envelope and membrane unstained. The 

 entire mass of the tubercles, composed of the infected leguminosa 

 cells and the infecting bacteria, has been called the bacterioid tissue. 

 The bacteria themselves, after infecting the higher plant cells, undergo 

 changes and degenerate into involution forms which have been 

 called bacterioids (this means bacteria-like forms). These are quite 

 pleomorphous, have branches and sub-branches, and often form a 

 more or less regular complete reticulum, or network. The nitrogen 

 content of the dry substance of these root nodules of leguminosse 

 is very high. It was estimated by Stoklasa, at the time of flowering 



