516 University of California Fublications in Agricultural Sciences [Vol. 1 



ing effect on the production of straw in the second crop becomes 

 apparent. The fact that the wide range of concentrations just 

 referred to is productive of similar effects seems to indicate 

 that most of ZnSO^ is adsorbed by the soil and but little of 

 it is free to affect the plant in the soil solution. 



With the exception of one or two doubtful cases, grain 

 production is somewhat depressed throughout the second crop 

 of the ZnS04 series. This appears to be even more true for the 

 first concentration of ZnS04, which stimulates straw production, 

 than for the higher concentrations, which depress straw pro- 

 duction. All of these judgments, however, are based on averages 

 of duplicate pots which do not agree very well, and hence con- 

 siderable caution is employed in stating them. Again, the effect 

 of ZnS04 on grain production seems to be about the same 

 whether small or large quantities of the salt are employed. 



So far as root production is concerned, however, the data 

 of the second crop in the ZnSO^ series are very different from 

 those bearing on the yields of grain and straw. With three 

 exceptions, two of them at the highest concentrations of ZnSO^ 

 employed, the latter induced the production in all pots of more 

 roots than were produced in the control pots. While in many 

 cases the stimulation in the direction noted was not great, it 

 was definite, and in many other cases it was very considerable. 

 Moreover, there was good agreement between tlie duplicate de- 

 terminations. The greatest stimulation to root production 

 occurred between 200 and 2600 p. p. m. ZnSO^. While, there- 

 fore, the second crop of the ZnS04 series differed from that of 

 the CuSO^ series with respect to grain production, there was 

 great similarity in action between the two as regards root yields. 



Thikd Crop 

 In the third crop of the ZnSO^ series, the toxicity of ZnSO^ 

 appears to have become augmented even over that of the second 

 crop. There seems to be no case of stimulation even in the 

 lowest concentration (200 p. p.m.). This applies to straw, 

 grain, and roots equally well. On the other hand, tlie toxicity 

 of ZnS04 for root and grain production by barley in the third 

 crop is certainly not very marked, although uniform. For straw 



