422 MAN BECOMES THE CONQUEROR OF THE WORLD 



PROBLEM I. WHAT ARE THE CHIEF RESPONSES OF 

 PLANTS AND ANIMALS? 



Demonstration 1. To show some tropisms in plants and animals. 



Grow some bean seedlings in a glass dish which is kept watered at 

 one side only. Grow some bean seedlings in unequal illumination. 

 Examine oxalis or clover at night and in the morning, in order to ob- 

 serve " sleep " movements of leaves. Touch a leaf of a sensitive plant 

 with a pencil. 



Place Euglena in a vessel with unequal light illumination. 



In the first two cases, note the arrangement of roots against the 

 glass side of the dish. What leaf movements of oxalis and sensitive 

 plant are noticeable? Where in the vessel do you find Euglena most 

 abundant? 



What forces act upon plants and animals? How do they affect 

 them? 



How plants and animals receive stimuli. In the simplest 

 plant and animal cells which live by themselves there are no 



specialized parts which are es- 

 pecially fitted to receive out- 

 side stimuli. The amoeba, for 

 example, is influenced by 

 temperature, food, and other 

 stimuli, but it has no sense 

 organs. Some tiny plant-like 

 animals (or animal-like plants) 

 such as Euglena (ti-gle'nd) have 

 a tiny structure called an eye- 

 spot, which seems to be more 

 sensitive to light than other 

 parts of the cell. 

 The more complex single- 

 cWoroplosti-g ^ „/l cytoplasm celled animals, as Paramecia, 



have parts of the cell (cilia) 

 more sensitive to touch than 

 other parts. Animals and, to 



Euglena. Would you call it a plant or an ani- a lesser degree, plants, as they 

 mal ? Give your reasons. , i . , . 



become more complex in struc- 

 ture, tend to have special parts set aside to receive stimuli. These 

 special parts of complex animals are called sense organs. 



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