28 MANUAL FOR SUGAR GROWERS. 



nitrate equal to one Imndred and thirty-three pounds 

 of nitrate of soda per million, thus proving that con- 

 dition and not manure was what this particular field 

 lacked. 



From what has been said, it follows that nitrate 

 of soda is practically the only nitrogenous manure 

 absorbed by the plant without having to undergo 

 change under the influence of the nitrifying mi- 

 crobe. 



Eecent researches have led to the conclusion that 

 plants belonging to the natural order Leguminosce, 

 which includes all plants of the pea and bean tribe, 

 take up their nitrogenous food in a different manner 

 from other plants ; they can apparently freely assim- 

 ilate nitrogen compounds other than nitrates, and 

 it has been found that the weight of nitrogen in a 

 leguminous crop may exceed the weight of nitrogen 

 in the soil and manure used before the crop was 

 grown. The inference is, then, that leguminous 

 plants, unlike others, can make use of the nitrogen of 

 the atmosphere. It is also found' that leguminous 

 plants have curious little swellings or nodules upon 

 their roots, varying in size and shape on different 

 plants ; on the pigeon-pea {Cajanus indicus) these 

 swellings assume large dimensions, sometimes being 

 an inch or more in diameter. The internal struc- 

 ture of these nodules, as far as they have been ex- 

 amined by the author, appears to be as follows : 

 There is an external layer resembling the bark of the 

 root ; immediately within this comes a cellular layer 

 traversed by fibro-vascular bundles; in the centre 

 of the nodule is a mass of cellular tissue (a, Fig. 6), 



