THE STRUCTURE OF PLANTS 27 



39. Organs and functions. From our laboratory study 

 we have learned that a common plant consists of roots, stems, 

 and leaves, and that at certain seasons of the year flowers 

 and fruits are present. To each of these various parts is 

 given the name organ. Roots are useful to a plant, for one 

 thing, because they hold it in the ground, while stems support 

 the leaves, flowers, and fruits. In fact every organ of a 

 plant has some work to do, and this work is called its func- 

 tion. Hence, we may define an organ as a part of a plant that 

 has a certain function or functions to perform. 



40. Microscopic structure of plants. When one exam- 

 ines by the aid of a compound microscope a small portion 

 of any of the organs of common plants, one finds that each 

 organ is composed of many smaller portions too minute to be 

 seen with the unaided eye. These tiny divisions are called 

 cells. We shall now attempt to become familiar by the use 

 of the compound microscope with the appearance of several 

 kinds of plant cells. 



41. Study of plant cells. Laboratory Study No. 21. 



Materials: (1) Slides prepared as follows : Cut a layer of an onion 

 bulb into small squares, and strip off from the inner surface of each 

 square a very thin layer. Place it on a glass slide and add a drop 

 of water. (If it is desirable to keep the slides for several hours, 

 put glycerin diluted with water over the onion cells.) Cover each 

 thin membrane with a cover glass. 1 (2) Prepared or freshly cut 

 thin sections of roots, stems, and leaves. 



1. By the aid of the low power of the compound microscope, 

 examine the slide prepared as directed in (1) under 

 materials. Note that the thin membrane is com- 

 posed of a large number of tiny spaces each in- 



1 The authors are indebted to Miss Elsie M. Kupfer, Head of 

 Department of Biology of Wadleigh High School, New York City, 

 for suggesting this admirable material for cell study. 



