PLANT CLASSIFICATION 169 



floating the mass in a saucer of water. A filament should then be 

 studied under the microscope, and the parts of a single cell described, 

 and several cells should be drawn. If fresh zygospore material can 

 be obtained, this should also be studied, and the parts described 

 above noted and drawn ; otherwise charts or pictures may be used. 



188. Pleurococcus and other algae. Another and still simpler 

 form of plant life is known as Pleurococcus. It may be readily 

 obtained from the trunks on the north side of 



large trees. It appears as a very thin green layer 

 closely adhering to the bark. If a little of this 

 material is scraped off and placed under the 



compound microscope, it will be found that it is , 



, , . ,. . , FIG. 86. Pleuro- 

 made up of a large number of tiny circular green coccus. (Sedg- 



cells which adhere to each other more or less, wick and Wil- 

 since in the process of reproduction one cell son ^ 

 divides to form two, each of which is considered to be an individual 

 plant. Thus the whole mass is made up of a large number of 

 one-celled plants. 



The Spirogyra and Pleurococcus are only two of a large number 

 of simple plants known as algae. They differ widely in form, but 

 none of them develop roots, stems, or leaves. Among the most 

 common algae are the marine forms known as sea weeds, of which 

 there are many kinds. 



189. Suggestions for the study of Pleurococcus. No. 68. As 

 indicated above, material for the study of Pleurococcus may be 

 easily obtained by removing pieces of bark from trees having a con- 

 siderable quantity of this plant on their surface. If collected in a 

 dry season, the bark should be placed under a bell-jar with sufficient 

 water to make the air moist, and allowed to stand for several days. 

 The place in which the Pleurococcus is found should be described, 

 and also the appearance of a mass of the plants. Single cells should 

 then be studied under the high power of the compound microscope, 

 and the cell and its contents described and drawn. 



D. Fungi. (See Chapter IX, 147-166.) 



