CELLULAR NATURE OF PLANTS 



31 



II. Draw a few of the cells, making sure to include in your diagram, at 

 least two differently shaped ones. 



Higher plants are composed of many cells, but certain plants 

 are very simple in structure. A green coating is frequently found 

 on the north side of many buildings and of most trees. This is 

 caused by the presence of thousands of tiny one-celled, green 

 plants called Pleurococcus. 



Problem. Study of Pleurococcus. 



I. Scrape some of the green material on to a slide, mount in water, and 

 study with low and high magnification. Describe the shape, color, and struc- 

 ture of the cells. 



II. Draw a single cell and a group of cells. Label cell wall, the very large 

 chloroplast which almost fills the cell, and the nucleus. 



III. Write a description of what you have seen and tell how Pleurococcus 

 differs from Elodea and narcissus cells. 



A typical green cell that is easy to study is Spirogyra. As it 

 floats on the surface of ponds, it looks like a tangled mat of 

 green threads or hairs. A 

 common name for it is pond 

 scum or frog's " spittle." 

 This latter name is given to 

 it because it is slimy in tex- 

 ture and is found in the same 

 habitat with frogs. Many 

 people at one time thought 

 that the frogs spit it out. 



Problem. Study of the cells 

 of Spirogyra. 



By means of forceps and a pair 



. A photomicrograph of the lower surface of a leaf, 



oi scissors detach a few strands ot 



Spirogyra. Mount them on a slide and cover with a cover slip. Focus 

 the specimen under the low power. 



