112 REPRESENTATIVE PLANTS 



diatoms. A useless experiment in water systems supplied 

 by wells, but almost certain to yield good results from lake 

 or river sources of supply. From some source obtainable, 

 make a temporary mount and study carefully the profusion 

 of objects that appear under the microscope. Examine as 

 many forms as you are able to find in the mixture. What 

 is the color? Observe that many are transparent (these are 

 dead). Use (Ip) or Qq)) as necessary. Observe the similarity 

 of the ends. If possible, study the same diatom on differ- 

 ent surfaces. Compare with a box and lid for similarity 

 of form. Eind, if possible, many fine lines. Draw the 

 various forms and varying views of the same form. Ob- 

 serve the free brown forms for a slow motion ; also that 

 some forms are attached by stalks. Consult the books re- 

 garding the cause of this boatlike motion. 



Fossil diatoms. Consult all the references to diatoms you 

 can find. What use is made of fossil diatoms ? What is 

 the substance in the diatom that makes it thus valuable ? 

 What is diatomaceous earth ? How do you account for the 

 great accumulations of this material ? What reasons can 

 you find for such peculiar cell structure ? 



Type 12. Red Seaweeds 



General statement. These often very beautiful forms of 

 algae are common along the shores of both oceans, and are 

 often seen mounted on paper as souvenirs of seashore visits. 

 They are often highly complex and exceedingly varied in 

 form. Unless well supplied with fresh material, the question 

 of reproduction will be out of place in the laboratory. Only 

 the more easily observed features will therefore be noted in 

 this exercise. 



Appearance. Observe the wonderful variety of forms 

 assumed, flattened, ribbonlike, filamentous, feathery, coral- 

 like, and decide what forms your specimens show. Also 



