366 



to straw of i :i.75, while varieties grown for a long time on sewage beds, 

 showed I :2.88. Wheat and rye behaved similarly. The amount to which 

 ripening can be retarded in extreme cases, was found for red mountain 

 wheat, which, sown on April 19th, ripened on irrigated fields on the 13th 

 of September, but on non-irrigated, on August 24th. Tliere was then a 

 difference of 20 days. 



Mention is made in another place of the disadvantageous effect of 

 chlorin compounds on the starch content of potatoes, and on other plants. 



The "coatin;/ with ooze and mud" is the most important injury in sew- 

 age disposal beds. Liquid sewage contains, besides great quantities of 

 sodium chlorid and other salts, many organic substances especially pieces of 

 paper, coffee grounds and the like. Six investigations of Berlin sewage in 

 1902, gave on an average : 



Organic Substances 0.030 per cent. 



Potassium 0.006 per cent. 



Sodium 0.022 per cent. 



Sulfuric acid 0.006 per cent. 



Chlorin 0.020 per cent. 



The pieces of paper and the organic substances dry up on the beds 

 into tough, thin, flat cakes, decomposing only with difficulty because of 

 their fatty content. Soaked with salts and organic substances,, these form 

 the ooze, which acts detrimentally to the soil. The high content in salts will 

 easily cause a leaching of the calcium through an exchange of bases. 



Analyses^ prove that, on sewage beds covered with ooze, calcium is 

 actually carried off. The calcium content amounted in 



upper surface sub-soil 



Normal soil 0.153 per cent. 0.031 per cent. 



The same soil, but covered with ooze. 0.122 per cent. 0.048 per cent. 



An application of calcium is, therefore, desirable in soils covered with ooze, 

 since its action improves the soil physically. 



The disposal of the above mentioned papery flat cakes, which ma\ 

 choke young plants, especially grasses, will have to be undertaken first of 

 all by harrowing, tearing and removing the rags. Nevertheless, in planting 

 the fields, great quantities get on to the soil and have an injurious effect. 

 The enrichment in organic substances, due to the ooze, may be recognized 

 from the loss when heated : 



Normal soil contained (in a friable condition) ... 1.994 per cent. 

 The same soil, covered with ooze 2.418 per cent. 



Vegetative experiments in pots showed that an admixture of ooze always 

 arrested growth, and an addition of quick lime did not overcome this re- 

 tardation. The arrestment in development did not show itself in the ap- 

 pearance of positive symptoms of disease, but only in the delayed sprouting 



1 Backhaus, loc. cit. p. 69 and p. 114. 



