120 JOURNAL OF THE 



formation of the knots occurs only on the youngest roots and 

 their branches. 



The knot-bacteria make their way through young c^U-mem- 

 branes into the root-hairs and epiderujal cells of the root and 

 multiply there at the expense of the plasmic contents of the cells. 

 After the bacteria have increased to considerable extent in the 

 root-hair they unite near the point into grape-like clusters of 

 colonies which lie very close together, become enveloped in a 

 tough, glistening membrane by means of which they are united 

 with the cell membrane of the root-hair. There arises now near 

 the point of the root-hair, on the inside of its wall, a glistening 

 knob-like projection. Around this bacteria knob curls the end 

 of the root-hair in the form of a shepherd's crook, or of a screw. 

 Out of this enveloping screw at the base of the root-hair grows the 

 bacteria-knob as a hypha-like or thead-like tube, which is sur- 

 rounded by a glistening membrane and filled with bacteria. From 

 this time on until the formation of the knot and the differentia- 

 tion of its tissue the bacteria-tube resembles a real non-septate 

 fungus filament: it grows at the apex and produces branches. 



After growing out of the enveloping root-hair the bacteria- 

 tube enters the epidermis of the root, pierces the rind and grows 

 sometimes so deep as the endodermis of the central cylinder. Id 

 its growth and branching it passes between the cells, splitting the 

 membrane between two cells and crowding the two lamelhe apart, 

 forming more or less prominent distended places in the tube, the 

 outside of which is bounded by the two lamelhe and the inside 

 filled with bacteria. The bacteria-tubes also send short branches 

 through the cell membranes into the cells which grow towards 

 the nucleus were formerly considered to be haustoria, and in 

 unstained preparations are very difficult to distinguish from the 

 cell contents. These Beijerinck* took to be the remains of 

 nuclear division. In the early stages of the development of the 

 knot no bacteria are found free in the contents of the cells; thev 

 are all enclosed in the bacteria-tube. 



*Die PapilionaceenknoIIchen, Bot. Zeit., p. 72G, 1888. Abstract in Bot. Centralblatt, Bd. 

 XX XVI 1 1, pp. 458, 459, 1889. 



