ROOTS 103 



97. ROOTS 



Object. To discover why strong fertilizers are harmful 

 to plants. 

 Apparatus. A potato, water, a knife, and saltpeter. 



Method. Cut the potato into thin slices. Make a 

 strong and a very weak solution of the saltpeter. Put some 

 slices of the potato into each solution and leave them for 

 an hour. Then remove them and examine them. How 

 do they differ? Why? 



Explanation. The weak solution, being good for the 

 plant, can be absorbed through its walls by osmosis ; but the 

 strong solution, being in need of more water, absorbs it from 

 the plant, so that the latter loses water instead of taking it up. 



Note. With very strong solutions there seems to be a sort 

 of toxic effect. 



Field Work 



98. COMMERCIAL FERTILIZERS 

 Object. To study the effect of fertilizers. 



Method. Procure samples of as many different ferti- 

 lizers as possible and apply them as follows: 



Plant as many plants as there are fertilizers and an extra 

 one for control. 



Treat each plant with one sort of fertilizer, being careful 

 to label each plant so that no mistake will be possible. Ob- 

 serve the growth during the season and compare results. 



Are all fertilizers equally good for all crops ? In all soils ? 



Talk with farmers and gardeners to find out what kinds 

 of fertilizers are best for each of the following crops: corn, 

 potatoes, tobacco, and wheat. 



What is done with soils which are too acid ? Too alkaline ? 



