526 University of Calif omia Publications in Agricultural Sciences [Vol. 1 



toxicity for barley of MnSO^ eveu when amounts of that salt 

 equivalent to 0.6 per cent of the chy weight of the soil were 

 used. On the other hand, the stimulating effect of MnSO^ for 

 barley in the first crop on the greenhouse soil appears to be 

 clearly evident. This is particularly true for the first three con- 

 centrations, amounting respectively^ to 500, 1000, and 1500 p. p. 

 m. At concentrations exceeding 1500 p. p. m. IMnSO^, the stim- 

 ulation is only slight, and three concentrations — namely, 3500 

 p. p. m., 4000 p. p. m., and 5500 p. p. m. MnSO^ — possibly de- 

 press barley growth to some extent. The latter effect can scarcelj^ 

 be taken as indicating definite toxicity, however, since, as above 

 pointed out, even the highest concentration employed (6000 

 p. p. m. MnS04) appeared to stimulate barley growth slightly, 

 and the toxic evidences referred to are noted at concentrations 

 which lie between slightly stimulating concentrations on both 

 sides. At anv rate, we have no evidence of the toxicitv of 

 IMnSO^ in tlie first crop until concentrations equivalent to 3500 

 p. p. m. of MnSO^ are reached. 



When the root and straw yields are considered separately in 

 the first crop, some interesting observations may be made which 

 are not possible when the dry matter is considered as a whole. 

 For example, stimulation to root development in the first crop 

 of the MnS04 series is apparent only in the first three concentra- 

 tions above noted as giving the largest yields of dry matter. 

 Moreover, the straw j^ields are also distinctly higher at those 

 same concentrations. But whereas MnSO^ gives evidence of 

 toxicity to root development, either slightly or definitely, at all 

 concentrations tried above 1500 p. p. m., it continues beyond that 

 concentration to be slightly stimulating to straw production. 



In comparison with the other salts above described, MnSO^ 

 is distinctly superior in the magnitude of its stimulating effects. 

 The only other salt which manifests some resemblance to 

 MnS04 in that respect is CUSO4. Since the concentrations 

 of these two salts here employed, however, are very different 

 from each other in the two cases, no more detailed comparison 

 would be wholly justified. 



