582 TRANSACTIONS OF SUB-SECTION B. 



solution was then obtained by mixing 5 grm. of this inoculated soil in 100 c.c. of 

 water with 1 grm. of sugar and incubating for twenty-four hours only; 50 c.c. 

 of this solution were then applied to pets containing 5 ounces of soil each, and 

 incubated at 24° C. for ten days. The nitrogen determinations yielded : — 



Mgs. N. per 

 100 grin. 



Soil+50 c.c. distilled water 324 



Soil+50 c.c. autoclaved culture 330 



Soil+50 c.c. living culture 359 



An increase of 35 mgs. nitrogen per 100 grm. of soil, which represents an increase 

 of about 350 lb. of nitrogen per acre, taking an acre of soil 4 inches deep as 

 weighing 1,000,000 lb. 



To further test the effect of the mixed culture (both pure culture and soil 

 culture) under ordinary conditions on different soils a number of shallow plant- 

 dishes, each containing 3 lb. of soil and inoculated with 300 c.c. of the culture, 

 were kept in one of the greenhouses at the Chelsea Physic Gardens for fourteen 

 days. Analyses of these gave the following averages : — ■ 



Soil A Soil B Soil C Soil D 



Mgs. N. per 100 grm. Soil 



Control 371 375 312 ~402 



Pure culture . . . .403 396 336 421 



Soil culture . . . .406 395 333 424 



Increase. 

 Pure culture .... 32 21 24 19 



Soil culture .... 35 20 21 22 



Experiments in progress indicate that this fixed nitrogen is readily assimilated 

 by plants, and crops are benefited by an application of the mixed culture. 



4. Notes on the Nature of Nitrogen Fixation in the Root Nodules of 

 Leguminous Plants. By John Golding, F.I.C. 



Nearly a quarter of a century has elapsed since Hellriegel and Wilfarth 

 showed that leguminous plants are able to assimilate the free nitrogen of the 

 atmosphere when nodules are developed on their roots ; but the problem of what 

 takes place in the root nodule is still unsolved. 



Numerous researches have led to the following conclusions : — ■ 



(1) That the plant is able to get all its nitrogen from the air of the soil, and 

 that the quantity fixed is very large. 



(2) That the nodule is the seat of the process. 



(3) That fixation is accompanied with a change in the form of the organism, 

 which invades the root hair as an infection thread, passes through a rod-shaped 

 stage, and finally assumes the' (Y) bacteroid form. 



(4) That practically each plant has its own nodule organism, and though the 

 differences seldom amount to a difference of species, it takes a considerable time 

 for the nodule organism of one plant to become adapted to another plant, and 

 when so adapted it is not capable of infecting the plant from which it was first 

 taken. 



(5) That this adaptation to a particular kind of plant is retained by the 

 organism in the soil for a considerable period, during which assimilation, if it 

 takes place at all, is much less than when the organism is in the nodule. 



The conditions which obtain in the nodule are as follows : — 

 The acidity of the cell sap must be contended with. Nitrogenous products 

 of growth must be removed at an early stage of development of the plant. The 

 organism must be fed with some carbohydrate, to give it the necessary energy to 

 fix the nitrogen. Some limiting factor must restrict the number and size of' the 

 nodules. Chemical differences must exist between the roots of nearly related 

 plants to which the organisms must be very sensitive. The atmospheric conditions 

 obtaining in the nodule may also differ from those in artificial cultures. 



