PHYLOGENY 



Figure 39. A Club Moss, Lijcopodium, Including an Enlarged 

 View of a Single Stem. ( From Weatherwax, "Plant Biology," 2nd 

 Ed., W. B. Saunders Co., 1947. ) 



chlorophyll. When the microspores are released, they fall down onto the 

 lower sporophylls. When wet by rain or dew the microspore wall splits 

 and sperm are released. These swim to the archegonia of the female and 

 fertilize the eggs while the female gametophyte is still contained in the 

 spore wall, and hence in the parental sporophvte. The embryo is thus 

 produced in the female gametophyte while the latter is still contained in 

 the sporophyte, a condition very similar to that of the seed plants. 



One might expect that a group with so many progressive characters 

 would have produced further, more progressive descendants, but this has 

 not been the case. The Lycopsida are a terminal group. Soon after its 

 origin, the group produced the dominant plants of the coal swamps, but 

 these became extinct before^ the end of the Paleozoic Era, and only four 

 gi'uera of small, insignificant Ivcopods have survived to the prc>sent. These 

 are often referred to as living fossils because their closest relatives are 

 long-extinct plants. 



Subphlyum Sphenopsida. The Sphenopsida, the horsetails, have played 

 a smaller role in the history of the plant kingdom than the Lycopsida. Like 



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