PLANT FOOD AND MANURES 133 



compare their total weight with that of the twelve seeds 

 sown in the pot. 



This experiment should teach us that plants cannot 

 thrive very long if supplied with nothing else but water, 

 for they are unable to make any use of sawdust as a 

 food. 



When plants are grown under these conditions, does 

 it make any difference whether they are in the light or 

 not? This experiment if carried out carefully should 

 answer this question. 



The above experiment can be usefully extended by 

 growing some plants in sawdust with the addition of 

 water only, others in sawdust watered with a solution 

 containing all the essential things for plant growth, and 

 others in ordinary good soil. 



A useful plant food solution for this purpose is the 

 following : 



Calcium nitrate . 4 grammes or about 60 grains. 



Potassium nitrate . I gramme 15 

 Magnesium nitrate . 1 5 



Potassium phosphate . 15 



Iron chloride . . one or two drops. 



Water .... 3 litres or about 5 pints. 



Place as before some plants in the dark, and others 

 in sunlight, and note carefully their growth and appear- 

 ance in each case. Also dry and weigh a certain 

 number of seedlings from each set of experiments, and 

 compare their weights. 



These two sets of experiments should teach us the 

 importance of light and plant food to the life and growth 

 of plants. 



