518 University of California Puhlications in Agricultural Sciences [Vol. 1 



of FeSO^ which did not yield increased growth of barley. This 

 constitutes the most striking set of stimulations noted in the 

 series thus far discussed. Moreover, we find again an evident 

 lack of relationship between the amount of FeS04 employed 

 and the degree of stimulation induced thereby. In agreement 

 with the results obtained in the CuSO^ and ZnSO^ series, the 

 FeS04 series yielded no grain worthy the name in the first crop. 

 Again in agreement with the results of the other series, consider- 

 able discrepancy was found in duplicate pots so far as yields are 

 concerned. In the case of the root yields, we have also large 

 discrepancies between duplicate pots. However this may be, 

 the straw yields in the treated pots of the first crop surpass 

 those of the untreated pots in almost all cases, even if the higher 

 figure for straw yields of the control pots be employed as a cri- 

 terion. This is not so for the yields of roots ; and while aver- 

 age yields show definite stimulation by FeSO^ for root produc- 

 tion of barley plants on the greenhouse soil, single values from 

 duplicate pots do not justify any conclusions of that nature. 

 Despite all this, there is certainly no reliable evidence of definite 

 toxic effects on the part of FeSO^ to barley plants under the 

 conditions of this experiment. In general, therefore, the results 

 of the FeSO^ series are not unlike those of the CuSO^ series, 

 and the ZnS04 series on the greenhouse soil so far, at least, as 

 the first crop is concerned. 



Second Crop 



It will be remembered again that the amounts of FeS04 

 employed for the first crop were doubled before planting the 

 second crop. On studying the yields of the latter, one is at 

 once struck by the strong parallelism in effect exerted on the 

 barley plants by ZnS04 and FeS04 in the second crop. Both 

 stimulate total dry-matter production in the very low concen- 

 trations and yet the discrepancies between the actual amounts 

 of salts used in the two cases are of course very large. Besides, 

 both seem to stimulate root development and, very slightly, the 

 production of straw, at certain concentrations. Again, there 

 appears to be indirect evidence that most of the salt applied is 

 not only rendered insoluble, as is probably- the case with FeS04, 



