HOW PLANTS OBTAIN THEIR LIQUID FOOD. 41 



weight ? Can plants remove all the moisture from the soil by absorption 

 through their roots ? 



Demonstration 1 5a (or Exercise). 



78a. To demonstrate the action of a root hair. — Take a long potato, cutoff 

 the ends squarely, and bore a smooth hole 

 from one end nearly through to the other 

 end, being careful not to split the potato. 

 Now pare off the sides to make a tube closed 

 at one end. Rest the closed end in a vessel 

 of water, as shown in fig. 25a, after having 

 filled the tube with sugar. After five or 

 six hours examine. The sugar inside of the 

 potato tube draws water inward from the 

 vessel, imitating the action of a root hair. 



Exercise 1 8. 



79. Salt particles cling to root hairs.- ^ Potato J^'^al cavity con- 

 Have at hand small pots of seedlings the taining sugar, standing in vessel of 



., r .... t, it i- water. B, section of potato tube 



SOll of which IS not wet. Full, Or dig, up a showing cavity only partly filled with 



seedling. Observe the soil clinging to the su S ar - < After MacDougal.) 



roots. Agitate it to remove as much of the soil as possible. Wash the roots 



by rinsing in water. Are all the soil particles removed ? To what portions 



of the roots does most of the soil cling ? Why ? Compare with seedlings 



grown in a germinator free from soil. 



III. Strong Solutions of Plant Food are Injurious. 

 Exercise 1 9 (or Demonstration). 



80. To show the eftect on plants of food solutions which are too strong. — 



Potassium nitrate is one of the food substances used in the water cultures. 

 It is also one of the necessary food substances from which nitrogen is 

 obtained for the plant. Take strongly concentrated solutions, say a 5$, a io#, 

 and a 20$ solution. Label three pots of seedlings to correspond with the 

 solutions. Pour in enough of each solution to the corresponding pots to 

 saturate the soil. In the course of three or four hours (or later) observe the 

 result. Observe the condition of the stems at the surface of the ground. 

 Explain the result in each case. Permit these to remain without watering 

 for a day to see if they will revive. Pour in water and wash through 

 to remove as much of the salt as possible. Set them aside for a day or two. 

 Do they revive ? Why ? 



