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



the higher concentrations of PbSO^. As was the case with some 

 of the other salts in other crops, PbSO^ seems to be toxic in 

 the third crop at the low concentrations at which it stimulated 

 growth in the second crop. On the other hand, it stimulates 

 gro\\i:h as above stated in the third crop at some of the higher 

 concentrations at which it was toxic in the second crop. 



However, most of the stimulating influence of PbS04, and 

 perhaps all of it, in the third crop affected the straw production 

 and not the root yields. This is again at variance with the 

 results obtained in many of the other series above described, in 

 which the usual condition was a parallelism between the effects 

 exerted by a salt on the different fractions of the total dry-mat- 

 ter jdelds. Thus very good straw yields were obtained in most 

 of the pots of the series in the third crop and instances of in- 

 creases over those of the control pots were numerous, but no 

 definite evidence of such stimulation in the case of the roots 

 could be noted. In the case of the grain, on the other hand, the 

 higher concentrations of PbSO^ seemed to be as definitely stim- 

 ulating as they did in the case of the straw yields. This is 

 in almost entire harmony with PeSO^ in the third crop, but 

 has little resemblance to the corresponding CuSO^ and ZnSO^ 

 series. 



Potash Alum — Greenhouse Soil 



This salt was tested in these experiments because it had been 

 proposed that if it was not detrimental to soils and crops, it 

 could be employed as a source of potash for fertilizers. It could 

 be cheaply obtained in all probability by treating granitic rock 

 containing adequate percentages of potash, with HoSO^, wliich 

 can be manufactured in large quantity by the important smelter 

 plants through the oxidation of SO2 fumes. In view of the 

 foregoing, potash alum was applied, as indicated in tables 

 Villa, VIII&, and VIIIc, which are given below, on the basis of 

 a certain number of pounds per acre, beginning with 300 pounds 

 KoO per acre in the form of KAl(S04)2.12HoO and going up 

 to 2000 pounds KgO per acre in the same form. 



