Nov. 8. 191S Relation of Sulphur Compounds to Plant Nutrition 247 



be out of place to include further data on that subject. Work has been 

 done especially on clover and rape. Data illustrating this influence are 

 given in Table IX. The crops were air-dried. 



Table l^i.— Influence of supply of sulphates on the sulphur and potassium content of 

 clover and rape 



As has been pointed out, the effect of a more concentrated soil-sul- 

 phur solution is to increase the total sulphur content of the root and the 

 stem, but not of the seed. This influence is particularly great in the case 

 of the leafy plant like the rape, but is not so marked in the red clover. 

 In the rape the percentage variation of sulphur ranged from 0.20 to i, 

 depending upon the supply, while in the clover the rarKge was from o.io 

 to 0.20. In the case of one crop of clover there is included the total 

 potassium content of this crop. It has been common, since the time of 

 Boussangault, to explain the action of calcium sulphate in the soil as a 

 liberator of potassium, and its effect as indirect. This explanation might 

 still be used for our own results where calcium sulphate was added alone. 

 In this case the growth of crop was so much increased over the growth in 

 the control that the total potassium removed was considerably more than 

 in the control. But where the complete fertilizer containing potassium 

 chlorid is compared with the complete fertilizer plus calcium sulphate, 

 such an explanation for the action of calcium sulphate becomes untena- 

 ble. The increased growth due to the calcium sulphate in the presence 

 of a complete fertilizer containing potassium can have no other explana- 

 tion than that its action was direct rather than indirect. 



SUMMARY 



The data presented from these greenhouse studies with one type 

 of soil indicate that certain plants are measurably increased in their 

 growth by the addition of sulphates. We have emphasized in another 



