520 rinvt'r.sit}/ of California Publications in AgrintUural Sciences [Vol. 1 



copper, zinc, and iron salts, PbSO^ was applied once only prior 

 to planting' tlie first crop. 



First Crop 



Like ZnSO^ and FeSO^, the PbSO^ was tested in the green- 

 house soil only. The yields obtained in the PbSO., series are 

 given in table Vila, VII&, and VIIc. The}- will be discussed 

 in conjunction with the comment already made with reference 

 to the aspect of the plants in the PbSOj series. It will be noted 

 there that the plants possessed little rigidity, Avere deep green 

 in color, and in general assumed a sprawling or prostrate, in- 

 stead of an erect, habit of growth. Tliis was a result of some 

 specific reaction of PbS04 and was exerted even though only 

 small quantities of the salt could have existed in the soil solu- 

 tion, owing to the insolubility of the salt. It should also be 

 observed in this series, as it has been in the others, that the 

 quantity of PbSO^ employed seemed to have little relation to its 

 toxic efi^ects on the yields of straw. The lack of grain produc- 

 tion has already been explained in other discussions above and 

 is connected not with any salt treatment, but with the condition 

 of the greenhouse soil itself, of which more detailed discussion 

 has been given. 



Root production was particularly affected in a deleterious 

 manner by PbS04 in the first crop. Roughly speaking, it was 

 reduced in the PbSO^ treated pots by more than 60 per cent 

 of the jdeld obtained on the untreated or control pots. In other 

 words, in this series, as in many others, root production and 

 straw production run almost parallel. This is further evidenced 

 by the uniformly depressing effect of PbS04 regardless of the 

 quantity in which it was employed. We find therefore in PbSO^ 

 (and in Pb, because all the sulfates used have a common anion) 

 a substance which in the first crop on the greenhouse soil exhibits 

 characteristics totally different from those of copper, zinc, and 

 iron under similar circumstances. Thus while the three salts 

 last named show definite powers of stimulating barley growth 

 in the first crop on the greenhouse soil, lead very markedly 

 depresses the growth of that plant under the same conditions. 



