WATER IN THE PLANT 73 



ear stage, about 80 per cent of the substance is water. 

 A fresh turnip is over 90 per cent water. Fresh wood of 

 the apple contains about 45 per cent of water. The plant 

 secures its water from the soil. 



REVIEW. What is plant-food ? Where does some of it come 

 from? Describe the feeding root. Describe root-hairs. What is 

 their function? How does the root- hair differ from the rootlet ? 

 What is osmosis? Describe the experiment. How does the soil water 

 get into the root-hair? For how long does this absorption continue? 

 Under what conditions may the root-hair lose its sap? In what condi- 

 tion must the soil water be in order to be absorbed ? What may result 

 if the food solutions are too strong? Has this fact any interest to the 

 plant -grower? What is root -pressure? How is the water held in the 

 soil when it is most valuable to the plant? How are plants able to 

 live in dry soil ? Why do roots need air? How do they get it? Describe 

 what effect a cold soil has on roots. How do roots secure the plant- 

 food in the soil particles? What elements are necessary to plants? 

 In what forms must these elements be in order to be absorbed by the 

 roots? About what percentage of the whole substance is ash ? What 

 is the most abundant constituent in plants? Whence does it come? 



NOTE. Examine soil under a lens, to see the odd and miscel- 

 laneous particles of which it is composed. 



Not all kinds of plants exhibit strong root-pressure. The grape 

 vine is a good subject to show it. If pot plants are used, choose a 

 well-rooted one with a straight stem. Coleus, begonia and Impatiens 

 Sultani are good subjects. These can be had at greenhouses. 



Root excretions may etch a marble surface. 



