ROOT-NODULES OF LEGUMINOSAE. 103 



All those plants which had not received nitrates showed nitrogen-hunger early (about time 

 of appearance of third leaf). By June 28, the plants inoculated with the unboiled soil-extract had 

 recovered from their nitrogen-hunger and grew rapidly from this time on. This increased growth 

 of the plants in the upper row was correlated with the presence of nodules on the roots of each one 

 of the plants. There were no root-nodules on the plants in the lower row. 



The total grams of dry substance from the upper row (28 plants) was 106.542 ; the total grams 

 from the lower row (32 plants) was 1.888. 



According to Tschirch (1887) the filaments possess no membrane but only a hyaline border layer 

 and, therefore, have nothing in common with fungous hyphae; they are not of a fungous nature. It 

 is very unlikely also that they are plasmodial strands. Tschirch saw and figured the trumpet-like 

 expansions where the filaments penetrate the cell-walls. He believed the membrane was not pene- 

 trated. The bacteroids probably are not given off from the filaments. Their variable form is opposed 

 to the view that they are of bacterial origin. It appeared to him rather that the filaments decomposed 

 and then later the bacteroids were developed out of the cell plasma. The filaments and bacteriods 

 are held to be two stages in the differentiation of the cell-contents of the plant itself. The nodules 

 are considered as transitory reserve tissue, especially for albumen ; possibly also starch. 



Marshall Ward's communication on this subject was read before the Royal Society of London 

 in June 1887, and appears as the last paper in the Philosophical Transactions which was published 

 in 1888, that is at about the same time as Beyerinck's paper in the Botanische Zeitung. 



Ward obtained numerous infections in water-cultures by binding on slices of the root-nodules. 

 He saw and figured the entrance of the organisms through the root-hairs in the form of filaments 

 or tubes, as he calls them, and the penetrations of these filaments through the cortex into the tissues 

 where he observed, figured and described the characteristic branching. He also saw the bacteria 

 and bacteroids within the cells. He interpreted the whole phenomenon as one of fungous infection. 

 He regarded the parasite as related to the V ' stilagineae and considered the bacteroids to be yeasts 

 budded from special portions of the hyphae. His description is so full and his figures so distinct that 

 there can be no doubt of his having meant them to apply to this organism. Most of his studies were 

 made on the broad bean, Vicia faba. 



His cultural work did not lead to any satisfactory results. In his second paper, published in 

 1890, he says: 



"I may here say that these cultures (i. e., as micro-cultures) have given me much trouble, and 

 little results. To obtain pure cultures is a matter of greater difficulty than Beyerinck's paper would 

 lead one to expect, and it is not proposed at present to lay much stress on the evidence got from them." 



This second paper figures the entrance of the organism into the root-hairs. First a bright spot 

 appears near the apex of the hair, and from this a little later a filament projects into the interior, 

 and grows toward the cortex. The root-tip curves. 



Following Woronine, Beyerinck in Holland was the first man to recognize clearly the nature of 

 the organisms occurring in root-nodules of Leguminosae. These he designated Bacillus radicicola. 

 His long paper in Bot. Zeit., 1888, called general attention to this subject. The following are some 

 of the statements made in this paper: 



The splitting of the primary bark for the emission of the side roots is the special means of 

 entrance of B. radicicola. The bacteroids stain like B. radicicola but not intensely. They are of 

 various shapes, branched, round, pear-shaped or bacteria-shaped. They are incapable of growth. 



Melampyrum pratense has root-nodules containing bacteria (DeVries, Beyerinck). Beyerinck 

 says such nodules also occur on Rhinanthus major and on the roots of Alnus, Eleaginus, and Myrica. 



While the bacteroids can be found in nearly every cell of the nodule, and occur also in the bark 

 and epidermis of normal roots, the interior of the central cylinder is the special tissue of the bacte- 

 roids (see fig. 34). 



"The bacteroids are organized albuminoid bodies which the plant has formed out of Bacillus 

 radicicola, for the purpose of local storage of albumen therefore an organ of the plant protoplasm, 

 developed from bacteria which have wandered in." (Column 732.) 



Two types of nodule are recognized one in which the bacteria gain the ascendency and destroy 

 the interior, they themselves remaining alive; the other, in which the nodule, i. e., the host plant, 

 gets the advantage ; the bacteria being converted mostly into bacteroids, incapable of growth and 

 furnishing food for the plant. He calls those nodules normal in which no bacteria remain capable 

 of germination, except perhaps in the meristem. 



The small threads which pass from cell to cell he considered to be remnants of the nuclear 

 spindle. Sometimes when the bacteria get the upper hand, nucleus and cytoplasm are destroyed. 



Beyerinck distinguishes three sorts of bacteroids: (i) normal, (2) a smaller sort called "hem- 



