138 CLOVER CULTURE. 



could not long remain unsuspected, and numerous, long- and 

 carefully conducted examinations only . served to confirm the 

 investigator in the certainty that tubercles and power were 

 closely correlated. Tubercles and power was the law, while 

 also no tubercles and no power was also a law. There was 

 no visible cause for the tubercles. What was more natural 

 for the scientist than to suspect an invisible cause. Recent 

 discoveries in other fields suggested that probably the tuber- 

 cles were of bacterial origin. To determine this, wadding r 

 which lets in air, but strains out bacteria, was placed over 

 the pots. The result was that no bacteria could get in,, 

 hence, no tubercles were formed, hence, no nitrogen was 

 taken up, hence, no thrift in the plant. Nitrogen hunger,, 

 nitrogen starvation, was nature's answer to the question of 

 the experimenter. 



Pursuing his investigations further, Prof. Helriegel 

 found that some pots left uncovered thrived, others did not, 

 and none covered with wadding did. The scientific infer- 

 ence, therefore, was that whether they throve or not depended 

 on whether bacteria found an entrance by chance. Another 

 equally clear inference was that the ground where clover, 

 beans, peas and other legumes had grown must be full of it. 

 This was readily tested by placing soils in which these plants 

 had grown in the vessel with water, and after the sedimen I 

 had all settled to the bottom, and the water had become clear , 

 decanting carefully so as to take nothing but the clear water . 

 He then watered the plants that were drooping from nitroge n 

 hunger, and straightway every plant thus treated developed 

 tubercles and acquired the power of securing nitrogen, when 

 there was none in the soil in which it grew. He then too b 

 of the same water and sterilized it by boiling to kill all th e 

 bacterial life, watered the plants with this, protecting them 

 by wadding from accidental bacterial inoculation, and the 

 result was that no tubercles were formed, no power to take up 

 litrogen was developed and there was no thrifty growth. 



The illustration on the following page will aid the reader 

 n securing a clearer comprehension of what occurs as root 

 :ubercles are developed in the legumes. It is taken from the 

 Lehrbuch der Pflanzenphysiologie, by Dr. A. B. Frank, 

 professor in the Agricultural High i;jhool at Berlin. * 



Figure A in the illustration is a root of the lupine on 

 which are several root tubercles. Figure B is a section of a 

 *oot tubercle ; at f is seen the central woody-fibrous co rd 

 ind around it, within the root bark, the fleshy parts of t he 

 Dacterial tissue. Figure C shows the first stage of infecti on,, 

 which precedes the formation of the tubercles ; , e is the 



