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



our data for PbSO^ in greenliouse soil are reviewed in the light 

 of the foregoing-, they are found to ])e in accord with those of 

 Voelcker so far as the second and third crops of barley are con- 

 cerned. At some concentrations in both of those series, PbSO^ 

 acted as a stimulant to barley and often at very large or at the 

 larger concentrations used. Our results, however, are entirely at 

 variance with those of Jensen and Stoklasa in so far as the first 

 crop is concerned. In that series we noted nothing but evidences 

 of marked toxicity of the PbS04, with the accompanying effects 

 on the barley plants which are described. 



Potash Alum 



No literature has been found on the effects on plants of 

 potash alum in soil. The discussion set forth above giving our 

 results with that material will therefore have to suffice. 



Manganese 



With the possible exception of copper, manganese and its 

 effects on plants have received more attention at the hands of 

 plant physiologists and students of soils than any other element 

 here under consideration. Despite that fact, there would appear 

 to be as much contradiction in results obtained in this case as in 

 those of the other elements above studied. We find reports of 

 toxicity of manganese in solution cultures in the publications 

 of Aso,'-*^ Loew and Sawa,"* and Brenchley.''' On the other hand, 

 the results of the same authors also give evidence of the stimu- 

 lating effects of manganese at certain concentrations. Miss 

 Brenchley even hints at the possibility of the existence, simul- 

 taneously, of a toxic and stimulating effect on the part of man- 

 ganese and claims that either effect may show predominance, 

 depending on the concentration of the salt employed. 



On the toxic action of manganese to plants in solid substrata, 

 principally in soils, we have the reports of experiments of 



93 Bull. Col. Agr., Tokyo Imp. Univ., 5, p. 177. 



94 Bull. Col. Agr., Tokyo Imp. Univ., 5, p. 161. 



95 Inorganic plant poisons and stimulants, Cambridge, 1914. 



