H. B. Hutchinson and N. li. J. Miller 181 



suspending in an oil bath heated at 160 — 180'. The soil was next 

 extracted (in the pots) with water to remove nitrates, and again 

 sterilised. Nitrogen, in the form of ammonium sulphate and sodium 

 nitrate respectively, was added to the soil, sometimes both in larger 

 and smaller amounts. Occasionally ammonium phosphate was also 

 employed. Each series of experiments generally included pots which 

 had been neither sterilised nor extracted, as well as sterilised and 

 extracted soils without addition of nitrogen. During growth sterilised 

 water was supplied to the soil from below. Some time (not imme- 

 diately) after the conclusion of the experiments the soil was examined 

 for nitrates and in every case nitric nitrogen was found to be absent. 

 The results showed that whilst ammonium salts were directly assimi- 

 lated, without previous nitrification, the yields obtained with nitrate 

 were generally better, the advantage of nitrate over ammonium salts 

 being particularly marked during the early stages of growth. 



In an experiment with Oats in 1890, Pitsch found that all the soils, 

 at the conclusion of the experiment, contained ammonia (N. = 0001 5 to 

 0"0058 per cent.), and that this nitrogen, added to the nitrogen in the 

 plants, amounted to considerably more than was contained in the 

 manures. It was found moreover that the nitrate plants contained 

 more than twice as much nitrogen as was supplied in manure. So 

 that these plants evidently drew on the soil nitrogen, probably, for the 

 most part, in the form of ammonia, and partly as soluble humus\ 

 produced in the process of sterilisation. 



In his last experiments, Pitsch shows that additions of sodium 

 chloride to the pots manured with ammonium sulphate considerably 

 increased the yield. It would seem to be possible that the relatively 

 low yields obtained in most cases with ammonium salts may have been 

 in part due to unfavourable conditions as regards the mineral con- 

 stituents of the soil. 



The methods employed by Pitsch seem to be as satisfactory as 

 possible in experiments on so large a scale. It is evident that the 

 soils were not only thoroughly sterilised, but that the condition of 

 sterilisation was maintained. But although the results show that the 

 different plants grew in absence of nitrates, they fail to show that 

 the nitrogen assimilated was exclusively in the form of ammonia. 



In 1887, Frank (22) grew beans and sunflowers in water-cultures 

 containing nitrogen as ammonium salt and as nitrate. The solutions 



1 Compare H. W. Wiluy, Landw. Versuchs-Stat, 18'J8, 49, 193. 



13—2 



