24 



BOTANY 



Functions of the Parts of a Plant. — Still more prominent are 

 the structures we call flowers and fruits. Each of these structures 

 differs from each other part, and each has a different work or 

 function to perform for the plant. The root holds the plant firmly 

 in the ground and takes in water; the stem holds the leaves up to the 

 light; the leaves, under certain conditions, manufacture food for the 

 plant; the flowers form the fruits; the fruits hold the seeds, which in 

 turn reproduce young plants of the same kind. 



Organs. — Each part of a plant or animal, having a separate work or 

 function,is known as an organ. Most plants and animals are composed 



of organs; hence any hving thing, 

 even the simplest single living cell, 

 has come to be called an organism. 

 If we look rather carefully from 

 all sides at the organ called the 

 leaf, we find that the materials of 

 which it is composed do not ap- 

 pear to be everywhere the same. 

 The leaf is much thinner and more 

 delicate in some parts than in 

 others. Holding the flat, expanded 

 blade to the branch is a little 

 stalk, the petiole, which extends 

 into the blade of the leaf as a se- 

 ries of little veins which evidently 

 form a framework for the flat blade 

 somewhat as the sticks of a kite hold the paper in place. In the 

 same manner the veins, if cut crosswise and mounted on a glass 

 slide under the compound microscope,^ show that they are made 

 up of building material which, although microscopic in size, yet 

 differs considerably from other material in the same part of the 

 vein. The smallest units of building materia] of the plant or ani- 

 mal disclosed by the compound microscope are called cells. The 

 organs of a plant or animal are built of these tiny structures. 



Tissues. — The cells which form certain parts of the veins, the 

 flat blade, or other portions of the plant, are often found in groups 



* For a study of the compound microscope, see Hunter and Valentine, Manual, page 3. 



Section through the blade of a leaf, as 

 seen under the compound micro- 

 scope ; /, air spaces, which com- 

 municate with the outside air. 



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