EXERCISES WITH PTERIDOPHYTES 163 



not forget that the growing of ferns is an industry representing 

 many thousands of dollars. In past ages the ferns were much 

 more abundant and much larger than at the present time and 

 we are indebted to them, to some extent, for the enormous beds 

 of coal from which we secure most of our supply of fuel. (Chap- 

 ters* IX and XVIII.) 



EXERCISES WITH PTERIDOPHYTES 



1. Examine a fern carefully and note its roots, stem, leaves, sori and 

 indusium. 



2. Cut cross-sections of the stem and examine under a compound 

 microscope and note the points referred to in the text. Material for this 

 purpose can be preserved in alcohol or formaldehyde. 



3. Study the leaf in the same manner as indicated for leaf of the 

 Angiosperm. (Chapter IV.) 



4. Remove a sorus, crush and examine under the compound micros- 

 cope. Note the character of the sporangia as referred to in the text. 



5. Examine a prothallus with a hand lens or under a low power 

 of the compound microscope. Material for this purpose can usually be 

 secured from a neighboring greenhouse. 



QUESTIONS 



1. Where do you find the stems of the fern? 



2'. Compare the fern stem with the stems of a flowering plant. 



3. Compare the leaf of a fern with the leaf of a flowering plant. 



4. What do you find on the fern leaf not found on the ordinary leaf? 

 Reference. Read all you can about the formation of coal-beds. For 



such information see a good encyclopedia and works on Geology. 



