6 PLANT BIOLOGY 



Struggle for existence and adaptation to conditions are 



among the most significant facts in nature. 



The sum of all the conditions in which a plant or an ani- 

 mal is placed is called its environment, that is, its surround- 

 ings. The environment comprises the conditions of climate, 

 soil, moisture, exposure to light, relation to food supply, 

 contention with other plants or animals. The organism 

 adapts itself to its environment, or else it weakens or dies. , 

 Every weak branch or plant has undergone some hardship 

 that it was not wholly able to withstand. 



SUGGESTIONS. The pupil should study any plant, or branch of 

 a plant, with reference to the position or condition under which it 

 grows, and compare one plant or branch with another. With 

 animals, it is common knowledge that every animal is alert to 

 avoid or to escape danger, or to protect itself. 2. It is well to 

 begin with a branch of a tree, as in Fig. i. Note that no two 

 parts are alike (Chap. I). Note that some are large and strong 

 and that these stand farthest towards light and room. Some are 

 very small and weak, barely able to live under the competition. 

 Some have died. The pupil can easily determine which ones of 

 the dead branches perished first. He should take note of the 

 position or place of the branch on the tree, and determine whether 

 the greater part of the dead twigs are toward the center of the 

 tree top or toward the outside of it. Determine whether acci- 

 dent has overtaken any of the parts. 3. Let the pupil examine 

 the top of any thick old apple tree, to see whether there is any 

 struggle for existence and whether any limbs have perished. 4. If 

 the pupil has access to a forest, let him determine why there are 

 no branches on the trunks of the old trees. Examine a tree of 

 the same kind growing in an open field. 5. A row of lettuce 

 or other plants sown thick will soon show the competition between 

 plants. Any fence row or weedy place will also show it. Why 

 does the farmer destroy the weeds among the corn or potatoes? 

 How does the florist reduce competition to its lowest terms? 

 what is the result? 



