W.AI KK Cri,l I KKS. 



253 



Figure 12 (at right) shows the plants photograph- 

 ed as they grew in the solutions. The bottles are 

 covered with a thick black paper to protect the roots 

 from light. I he plants are growing in an extract of 



11. 1 (itati 



iiciwii ill wutiT I'xtnict lit' Kood soil. 



a soil that had grown potatoes for several successive 

 seasons and the yields had become very poor. No. 

 T is growing in the untreated extract of the soil. In No. 2 

 the extract has been evaporated to dryness, the organic mat- 

 ter charred and the residue redissolved in distilled water. No. 



