THE I'TKIUDOl'IIYTA 343 



778. Arc coinniou f(M-ns annuals or perennials? Why? 



779. Of wliat advantage to the fern plant is the indusium? 



780. Of what advantage is it to the fern plant to have the archegonia 

 and the antheridia on the same gametophyte mature at different times? 



781. In what particulars do the Ophioglossales resemble the ferns? 

 In what do they resemble the club mosses? 



782. Do you think that a cone is more pi'iinitiv(> tlian a group of 

 leaf-like sporophylls or not? Why? 



783. Of what advantage to the plant is it to have its sporophylls 

 grouped into a cone rather than scattered along the stem? 



784. How do a typical fern and a typical horsetail differ in the environ- 

 ment to which they are best adapted? 



785. What are the advantages of a subterranean, saprophytic gameto- 

 phyte over the free-living one characteristic of most ferns? Which 

 form do you think is the more primitive? Why? 



786. In what particulars does Isoetes resemble the ferns? In what 

 does it resemble the club mosses? 



787. In what particulars do the Equisetales resemlile the Filicales? 

 In what do they resemble the Lycopodiales? 



788. Of what significance is the fact that the gametophytesof ^'gwise- 

 tnm are usually dioecious? 



789. How do the elaters in the sporangium of Equisetum aid in spore 

 dispersal? 



REFERENCE PROBLEMS 



133. Of what cconoinic importance are the pteridophytes? 



134. Construct for Lijcopodium a graphic life-cycle similar to that given 

 in the text for a fern (Fig. 205). 



135. Construct a similar grapliic; life-cycle for Sddgiiiclld. 



136. Construct a similar graphic life-cycle for Equisetum. 



137. Give the derivations of the following terms and explain in what way 

 each is appropriate: 



Heterosporous Indusium Prothallus 



Sorus Annulus Sporophyll 



Strobilus 



