86 Effect of Manganese Compounds 



the vegetative growth only, a definite stimulus was obtained with a 

 higher concentration than in those experiments in which the plants 

 were allowed to form seed. This may or may not be significant, as 

 it is possible that seasonal variation and individuality of the plants 

 may have played some part. Barley seems to be most extraordinarily 

 sensitive to the action of manganese, as even 1 part in 100,000,000 

 was found to exercise a beneficial action (Fig. 18). With peas the 

 evidence of stimulus is less well marked. No sign of stimulation is 

 obtained until a greater dilution is reached than is necessary with barley. 

 Even so the resulting curves are not sufficiently conclusive to warrant 

 the definite statement that manganese does act as a stimulant to peas 

 when present in very small quantities (Fig. 19). 



(b) Stimulation in soil cultures. 



Roxas carried out pot experiments with rice in soil to which was 

 added varying proportions of manganese sulphate, with and without the 

 addition of nutrient salts of ammonium, potassium, and calcium. The 

 criterion of stimulation was the length of the growing leaves as measured 

 daily, a strength of M/1000 MnS0 4 (M = molecular weight) giving a 

 favourable result. 



In the Hills Experiments (1903) an increase of produce was 

 obtained with wheat by manuring with manganese phosphate, chloride, 

 sulphate, or oxide (Mn0 2 ), while an increase of straw was gained with 

 nitrate, though this compound decreased the yield of corn. With barley 

 no evidence of stimulation is set forth for any compound, except that 

 the root growth was improved by the addition of manganese iodide, in 

 spite of the general unfavourable action this substance exerted upon 

 germination and growth. 



Bertrand (1905) whose work will later be considered in detail, ex- 

 perimented on arable land, adding quantities of manganese sulphate (?) 

 equivalent to about 1'6 gm. Mn to each square metre, growing oats 

 from February to May. Increase of weight was found in the 

 plants growing on the manganese plots, the differences in favour of 

 manganese being 



For total crops 22'5 %. 

 grain only 17 '4 / Q . 

 straw only 26'0 %. 



A certain alteration in the quality of the grain was also noted 

 from the manganese plots, the weight per hectolitre exceeding that 



