76 SOIL CONDITIONS AND PLANT GRO WTH 



Manganese is considered by Bertrand to be a constituent 

 of oxidases, and, therefore, necessary to the plant ; minute 

 traces only are required, larger quantities being harmful. 

 Dr. Brenchley's water cultures (54^) show that barley benefits 

 by small doses of manganese salts, and a number of field ex- 

 periments in Japan and in Italy l have indicated some manurial 

 value. Bertrand regards manganese salts as " engrais com- 

 plementaires " (35). Field trials at Rothamsted, however, 

 gave negative results. 



Chlorine does not appear to be necessary to the plant in 

 large quantity ; indeed, Knop grew even the halophytes without 

 it. Maze" finds that small amounts are necessary, which, how- 

 ever, would not need to be added in manure, as rainwater in- 

 variably contains chlorides : at Rothamsted the amount of 

 chlorine brought down per acre averages 16 Ib. per annum, 

 the annual fluctuations varying with the rainfall between 10*3 

 and 24/4 Ib. 2 Voelcker finds that, on the whole, chlorides 

 are more toxic than sulphates at equivalent concentrations 

 (290). 



In small quantities both fluorine and iodine appear to in- 

 crease plant growth : this was first shown in Japan by Loew 

 (i8o<:) and Suzuki (277*2): it is also accepted in France by 

 Maze" (197). Gautier and Clausmann (102) go even further 

 and claim that a dressing of 5 kgms. of amorphous calcium 

 fluoride per acre was followed by increases in cereal crops of 

 5 to 1 8 per cent, and sometimes considerably more in the 

 case of root crops. 



Sulphur is an essential food constituent, and occurs in 

 plants, especially in cabbages and swedes, to a greater extent 

 than is usually recognised, the older analytical methods giving 

 low results (Hart and Peterson (127), Peterson (223)). Sul- 

 phates are present in rain and in soil, but further additions in 



1 The Japanese experiments are recorded in the Bull. Coll. Agric., Tokyo, 

 1906 et seq. (210), and the Italian experiments in the Studi e Ricerche di 

 Chimica Agraria, Pisa, 1906-8 ; pot experiments have also been made by J. A. 

 Voelcker at the Woburn Experiment Station (Journ. Roy. Ag. Soc., 1903, 64, 

 348-359). See also E. P. Deatrick, Cornell Mem., 1919, 19, 371. 



2 E. J. Russell and E. H. Richards, Journ. Ag. Sci., 1919, 9, 309. 



