PLANTS AND THEIR ENVIRONMENT 609 



What causes roots to turn downward? Compare these plants with 

 plants growing in soil. What other changes have taken place? 

 Might these changes be due to changes in the environment? 



Demonstration 2. What substances are necessary for plant 

 growth ? 



Partly fill five jars, the first with distilled water, the second with 

 nutrient solution x without potassium nitrate ; the third with nutrient 

 solution without calcium phosphate ; the fourth with nutrient solution 

 without ferric chloride; and the fifth with nutrient solution. Place 

 in the jars corn seedlings with their roots in the liquids. Keep them 

 under observation for two or more weeks. In which jar does the 

 most vigorous growth take place ? What has soil environment to do 

 with plants? 



Demonstration 3. How may different foods affect an animal? 



Feed two white rats for several weeks upon the same amounts by 

 weight of gluten feed plus water and gluten feed plus milk. 



What differences do you notice in the appearance and weight of the 

 rats at the end of this period ? Do differences in composition of foods 

 have an effect upon rats ? 



Plants and their environment. Numberless examples of the 

 effect of the environment upon plants and animals are known to 

 all. Besides those just given, the familiar bleaching of celery 

 or lettuce when the sun is kept from them, the changes in the size 

 and color of plants having little or much exposure to the sun, the 

 effect of lack of water on plants, especially in a country where 

 irrigation is practiced, all these and more are everyday examples. 



But the scientist goes even further with his experiments. Bon- 

 nier, a French botanist, divided a dandelion plant and planted 

 part of it at a high altitude in the mountains, while the other part 

 was planted in the valley. Two quite different plants resulted. 

 Two lots of corn produced from seeds from the same cob, one 

 lot planted in wide rows and the other crowded, will be astonish- 

 ingly different. Under certain conditions environment seemingly 



1 A nutrient solution known as Sach's solution may be made as follows : 



Potassium nitrate 1.00 gram 



Sodium chloride 0.50 gram 



Calcium sulphate 0.50 gram 



Magnesium sulphate 0.50 gram 



Calcium phosphate 0.50 gram 



Ferric chloride 0.005 gram 



Distilled water 1000.00 grams 



Add the ferric chloride at the time the solution is to be used, by adding a drop 

 or so to the solution in the bottle used for the seedlings. 



