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 (54a) show that barley benefits 

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

 periments in Japan and in Italy ^ 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. Maz6 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 lb. per annum, 

 the annual fluctuations varying with the rainfall between 10 '3 

 and 24*4 Ib.^ Voelcker finds that, on the whole, chlorides 

 are more toxic than sulphates at equivalent concentrations 

 (290). 



In small quantities hoth. Jluorine and iodine appear to in- 

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

 (180^) and Suzuki (277^): 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 18 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 



^ 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 {yourn. Roy. Ag. Soc, 1903, 64, 

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



*E. J. Russell and E. H. Richards, Journ. Ag. Set., 1919, 9, 309. 



