CHAPTER XVIII 



PHYLUM XII. CYCADOPHYTA 



THE CYCADS 



484. Like the two preceding phyla this one is a mere 

 remnant of a much larger group. All told there are only 

 about 140 living species belonging to six families, while 

 we know of as many more families whose species have 

 become extinct. Enough has been made out as to the 

 structure of living and extinct forms to enable us to 

 define the Cycad phylum as follows: 



485. Their archegonial gametophytes are so dependent 

 that they are enclosed in the megaspore, which is itself 

 retained in the sporangium; the antheridial gametophyte 

 is minute and free, and its tubular antherid typically 

 develops two or more multiciliated sperms; after fer- 

 tilization of the egg the megasporangium becomes a 

 ''seed." The sporophyte is first enclosed in the seed, 

 where it is nourished by the gametophyte, and later it 

 escapes by developing roots below, and expanding its 

 leaves above; eventually some leaves become sporophylls 

 and develop microspores and megaspores. 



486. It is instructive here to compare the higher 

 Lycopods with the Cycads. In both there are micro- 

 spores and megaspores, and in both the microspores 

 always are set free from the sporangium. In both again 

 the microspore produces a very small (one- to few-celled) 

 gametophyte. However, the antherid of the higher 

 Lycopods is a few-celled structure, with many minute, 

 biciliated sperms, while in the Cycads the antherid is 



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