THE GROWTH RATE OF PLANTS 21 



the scale. Remove the plant from a warm to a cold room and 

 compare the growth rates. Compare the growth rate at 

 night with that of the same plant in sunlight. 



Water the plants in one pot with liquid manure, and 

 those in another with water to which has been added a 

 spoonful of ammonia. For a third pot use water to which 

 has been added a spoonful of commercial fertilizer. Com- 

 pare the growth rates of the plants under the different 

 treatments. 



Discussion: Some plants make very rapid growth and 

 mature a crop in a few weeks or months, while others require 

 a long growing period. The growth rate of plants in the 

 field or garden depends not only upon the kind of plant, but 

 also upon the temperature of the soil, the sunshine, and the 

 abundance of plant nutrients in the soil. 



Soils that have a sandy texture warm up more promptly 

 in the spring than heavy clay soils because they contain 

 less moisture. For this reason soils of a sandy nature should 

 be chosen for the growing of early truck crops and garden 

 vegetables. 



Manures and fertilizers applied to field and garden 

 crops increase their growth rate by furnishing food mate- 

 rials for the immediate use of the plants. 



