EXERCISE 28 



Eight or nine elements are present in the most common salts found in soil. These elements are 

 found combined, two or three being present in most of the salts. Thus, sodium chlorid (common salt) 

 contains sodium and chlorine ; potassium nitrate contains potassium, nitrogen, and 

 oxygen ; and so on. We saw that seeds can sprout without depending upon soil ; 

 yet something in the soil is essential to the growth of plants. 



Problem. Which of the substances in the soil are necessary for the continued 

 growth of plants ? 



What to use. Young plants grown from seeds, with roots carefully washed in 

 water ; eight wide-mouthed bottles with corks ; distilled water ; chemicals required 

 for a nutritive solution (p. 24 of Teachers' Manual). 



What to do. Prepare a nutrient solution containing all the salts given in the 

 formula. Prepare another solution from which one of the salts is omitted ; one from 

 which the second salt is omitted ; and so on. Observe growth and other changes from day to day. 

 Record. Enter the results in the proper spaces of the table on the next page. 

 Questions. 1. Which salt or salts would seem to affect growth ? 

 2. What other changes are brought about by the absence or presence of particular substances ? 



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