Biological Nitrogen Fixation 111 



that our successes, if any, reflect only the inevitability of 

 achieving them, once we entered the groove dictated by 

 the techniques. Even worse, these techniques for the most 

 part represent just about the only ones that could have 

 been used, so that the major contribution of the workers 

 in this field has been to provide the hands (or should I 

 say the feet?) to follow the path that led to a fertile area 

 for exploration. Such a point of view implies no criticism 

 of the investigators, for it is recognized that once an area 

 was discovered they exhibited considerable diligence in 

 its cultivation. This paper provides a few examples from 

 the studies directed toward investigation of the chemical 

 and enzymatic pathways that in one way or another illus- 

 trate this thesis. 



Case History I, Excretion of Chemical Intermediates 



It is appropriate that the first example should deal with 

 excretion of chemical intermediates, since the initial ex- 

 periments that led to this technique were made by Jacob 

 Lipman at the New Jersey Agricultural Experiment Sta- 

 tion. 



Let us consider the apparatus and methodology avail- 

 able to the plant physiologist in the earlier 1900's. Figure 

 1 illustrates the basic equipment used by Lipman (7). Ac- 

 cording to modern standards, it is not impressive; it con- 

 sists primarily of clay pots in which to grow plants. The 

 development of such plants could be conveniently esti- 

 mated by merely looking at them, but if the investigator 

 really wanted to be scientific, he could weigh the plants 

 or even determine total nitrogen. But if the apparatus 

 available consists of clay pots, one makes experiments in 

 clay pots. Lipman's experiments included some in which 

 leguminous plants such as peas and vetch were grown with 

 nonleguminous plants such as oats and rye. The white 

 sand used as substrate was supplied with all plant nutrients 



