In Brief 



The behavior of plants and animals appears to us as the fitting of or- 

 ganisms to the conditions under which they live; of course those organisms 

 which fail to fit the conditions soon cease to exist. 



Some of the adjustments which living things make to their environment 

 are fixed in their structure and development. 



Other adjustments appear to be the result of experience or of exposure to 

 new conditions. 



Plants show turning, or tropic, responses to gravity, water and light; 

 these appear to result from specific alterations in rates of growth. 



The bending of a plant toward the light is due to unequal growth, the 

 more rapid growth taking place on the darker side. The differential growth 

 appears to result from the action of light, which decreases the amount of 

 auxin, or growth-stimulating substance. 



The more we study the remarkable adjustments of living organisms to 

 their environment, the more of these adjustments do we find to be auto- 

 matic: the organisms cannot help responding as they do. 



Each particular kind of protoplasm thrives best in a particular set of con- 

 ditions; yet each is capable of adjusting itself to conditions that are some- 

 what different in one detail or another. 



The behavior of many species of animals in response to stimuli can be 

 conditioned or modified into new forms and patterns. 



Education consists in part of forming appropriate patterns of action or 

 avoidance. Habits are useful in doing things that have to be done in the 

 same way over and over again. 



Practice is effective in establishing habits when it is associated with strong 

 feelings. 



To meet new situations habits have to be subordinated to sound attitudes 

 and intelligence. 



EXPLORATIONS AND PROJECTS 



1 To observe the effect of light on movement within a cell, place a leaf from 

 the tip of a rapidly growing elodea on a slide and examine under the microscope 

 (use high power). Increase the intensity of illumination on the leaf by adjusting 

 the mirror so as to direct sunlight on it. Note effect on the streaming of the 

 protoplasm inside the cell. 



2 To study the growth movements, or tropisms, of plants: 



To find the relation of light to the direction of growth, place a pot of rapidly 

 growing seedlings under one-sided illumination; allow it to remain undisturbed 

 for several days. Note the position of stems and leaves at the start, and again 

 later. 



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