40 THEORIES ON THE ABSORPTION OF NITROGEN 



The culture of these bacteria in a free state in mineral 

 media has enabled us to grasp better the phenomenon of 

 nitrogen assimilation. Maze stated that, whenever nitrogen 

 assimilation took place, the liquid cultural medium became 

 more or less viscid. This is a characteristic of assimilation, 

 but the leguminous plant, by appropriating the bacterial 

 product for its own use, caused the viscid matter to dis- 

 appear as fast as it was produced. These experiments have 

 been confirmed by Buchanan and Greig Smith. 



J\I. Kayser sums up as follows: — 



" Fixation of free nitrogen in organic compounds and 

 formation of albuminoid matter are possible only when there 

 is accompanying destruction of substances containing 

 carbon." 



The Leguminos^ are all the more able to absorb the 

 contents of the nodules in view of the origin of the nodules 

 from the pericycle of the primary root, either opposite or 

 at each side of the wood bundles. The whole of the nitro- 

 genous bacterial product is absorbed by the Leguminosse; 

 following a check in the growth of the plants in question 

 the bacterial action gradually ceases. 



These bacteria, or a portion at least, return to the soil 

 and thus perpetuate their species. Nothing is known of 

 the form they take in the soil nor of "their spores; the isola- 

 tion of the bacteria of the Leguminos^e with the help of 

 soil solutions has never been satisfactorily accomplished. 



Judging from the whole of the experiments, Kayser 

 thinks the fact that the bacteria at first live at the expense 

 of the plant is well established. It is this period between 

 the moment when the bacterium penetrates the root hair 

 and its conversion into bacteroids that is the cause of the 

 familiar period of sickness in the Leguminos^e which lasts 

 until the formation of nodules is complete. Thenceforward 

 it is the plant's turn to live on the bacteria, for by that time 

 the bacteria have been converted into bacteroids and have 

 thereupon acquired the faculty of fixing nitrogen. 



