38 

 Soil treated with Ammonia 



I 



I "" "" ' ' I 



Black solution Insoluble humin 



Treated with Acid 



I 



r 1 . 



Solution Precipitate 



Mulder's apocrenic Humus 



acid Treated with Alcohol 



_I 



I " I. 



Solution Residue 



Hoppe-Seyler's Humic acid 



hymatomelanic acid | 



I Treated with Pyridine 



Melanin Compounds obtained | j 



by Schreiner and Soluble Insoluble 



Shorey humic acid humic acid 



The above procedure has been repeated with rotted straw and 

 with sugar humus, and in both cases similar fractions were 

 obtained. The residue afier pyridine extraction of sugar humus 

 was, however, only slowly soluble in ammonia, probably having 

 been converted into humin. 



SOIL ORGANISMS. 



XIV. L. M. Crump. " Niunhers of Protozoa in certain 

 Rothamsted Soils/' Journal of Agricultural Science, 

 1920. Vol. X. pp. 182-198. 



The method used wiis an improvement on that previously 

 adopted in this laboratory, but it did not discriminate between 

 active and encysted forms. Determinations were made at intervals 

 of about seven days of the numbers of total protozoa and bacteria 

 in the soil of Broadbalk Plot 2, which receives 14 tons of farmyard 

 manure in each year, and of Harpenden Field, which is typical of 

 poor arable land. The results are plotted on curves from a study 

 of which the following conclusions are drawn : — 



1. — Flagellates, amcebai and thecamoebae are usually present 

 in these soils in the trophic condition and in comparatively large 

 numbers, so that there is an extensive population actively in 

 search of food. 



2. — The protozoan fauna is practically confined to the top six 

 inches of the soil. 



3. — There is a definite inverse relation between the numbers of 

 bacteria and amoibae. 



4. — The am(jebae are uninfluenced by variations in the water 

 content and temperature of the soil and by the rainfall. 



5. — The richer the soil is in organic matter the richer it is in 

 protozoa, especially in amoebaj and thecamoebae. 



These conclusions are at variance with those arrived at by the 

 American investigators, but it is believed that the methods em- 

 ployed are l)etter than those used in America. 



