118 PLANTS AND ANIMALS 



45. The Needs of the Plant. 



We have learned quite a lot about plants and now we 

 are going to gather the information together. Science 

 study is different from some other studies because in 

 science we learn a number of facts concerning some- 

 thing and then gather all these facts together and try to 

 learn how they all are true at the same time. Then we 

 can form an idea of how the subject studied must act and 

 how it would act if conditions were different. This is 

 called drawing conclusions. Let us study an example : 

 We learned in Experiment 36 that air is necessary in 

 order that plant roots may grow. Since plants start 

 from seeds we might think that seeds would not sprout 

 if they were not supplied with air. If we nearly fill a 

 bottle with moist earth and plant a few beans or peas in 

 it, and then stopple it tightly, it will be found that the 

 seeds will not grow. Other peas and beans planted 

 under the same conditions in an open bottle will grow. 

 Then we can draw our conclusion that air is necessary 

 for plant life of any kind. How do water plants get air? 



We are always told to keep plants in a warm place 

 so that they may grow well. Do you think that if seeds 

 are not kept warm they will grow? Draw your conclu- 

 sions from the last paragraph and then try the exper- 

 iment. Place some seeds in moist loa'm and put it in the 

 ice chest, or try the experiment during cold weather. 

 Light, which is so closely connected with heat, is also, 

 necessary for green plants, as we learned in Section 11. 



In the germination tests, which you are making, you 

 are discovering that although water is necessary for 

 plant life, the plants die if they are supplied only with 

 water. They, like animals, require food and they obtain 



