WINDOW GARDENING 



and nitrogen are likely to occur in the soil in 

 insufficient quantities. Where the soil is defi- 

 cient in these forms of plant-food their lack 

 must be supplied by the use of fertilizers con- 



Fig. 14. The effects of exhausted soil 



taining them or else the growth of the plant be- 

 comes retarded and it fails to reach its normal 

 size and development. 

 Where the amount of soil for each plant is 

 50 



