530 University of California Publications in Agricultural Sciences [Vol. 1 



First Crop 



Table Xa shows the striking effects of concentrations of 

 MnCL on barley growth in the greenhouse soil during the first 

 crop. Whereas the first three concentrations of that salt, namely 

 500 p. p. m., 1000 p. p. m., and 1500 p. p. m., give verj^ marked 

 stimulation to barley growth (far more indeed than that given 

 b}" similar concentrations of MnS04), amounts in excess of 1500 

 p. p. m. MnClo are very markedly toxic. This toxicity increases 

 strikingly with the increase in concentration in MnCL beyond 

 2500 p. p. m., until at a concentration of 6000 p. p. m. almost 

 no growth is obtained. Even the difference between 1500 p. p. m. 

 and 2000 p. p. m. in the soil means a change from a high degree 

 of stimulation for barley production to a marked toxicity and 

 a decrease of about 50 per cent in the yield. No series of salt 

 concentrations studied by us and reviewed above gave anything 

 like the sharpness of manifestation of toxicity that is noted in 

 the first crop of the MnCL series. "We are evidently dealing 

 again with the acute toxicity of chlorine for living cells which 

 we have on other occasions pointed out in various connections. 

 This is true, if we may repeat again, despite the fact that at the 

 lower concentrations, chlorine ma}', as is strikingly exemplified 

 in table Xa, give astounding evidences of stimulation to barley 

 which surpasses any noted above with other and more uniformly 

 stimulating substances. 



When we study straw and root yields separately we find 

 that, in general, the effects of MnCL are similar with respect 

 to both in the first crop. The roots are, to be sure, only slightly 

 stimulated in growth in the first three concentrations employed, 

 whereas the tops are enormously stimulated. When, however, 

 the toxicity of MnCL becomes apparent, it is equally striking 

 in the roots and tops, as the figures in the table clearly show. 

 While in some respects, therefore, and particularly as regards 

 stimulation, the JMnCL behaves like the MnSO^ in the first crop 

 and the first three concentrations, it is totally different from the 

 latter salt in giving marked evidences of toxicity at concentra- 

 tions in excess of 1500 p. p. m. Nevertheless MnSOi still con- 

 tinues to stimulate growth, even though it does so very slightly 

 throughout the series. On the other hand, although the resem- 



