796 



BACTERIA : THEIR WORK 



of pentosans or allied carbohydrates are present. Besides pos- 

 sessing the power of utilising the free nitrogen of the air in the 

 manner indicated, this worker is of the opinion that the good 

 effect of the use of the organism is partially due to its power of 

 rendering soluble, and available to a cereal crop, some of the 

 insoluble nitrogenous compounds present in the humus and 

 similar decaying vegetable tissues present in the soil. 



Many experiments have been carried out with a view of 

 testing the practical utiHty of alinit in the cultivation of cereal 

 crops. The evidence in favour of its usefulness is very con- 

 flicting : some authorities state that 'it is of no practical value 



in any circumstances, while others, 

 holding that it gives no good results 

 upon poor sandy soils, consider that 

 it is advantageous when employed 

 for the growth of cereal crops upon 

 soil rich in humus. 



(iv) By leguminous plants living 

 in symbiosis with Pseudomonas 

 radicicola Beijk. 



If a well-developed bean plant is 

 carefully dug up from the field or 

 garden and the soil washed away, 

 a number of irregularly oval or 

 globular excrescences will be 

 noticed upon its roots (Fig. 264). 

 The structures are termed nodules 

 or tubercles. Each is pinkish in 

 colour, and in the early stages of 

 Faba L.) with nodules, «. (The figure growth of the bean plant are solid 

 ^uri:^agaaninNo™m^'r!r°"' and plump ; later they shrivel, and 



finally, when the bean has ripened 

 its seed, they decay or become brittle and break up into fragments^ 

 which are left in the ground with the remains of the bean's roots. 



