CHAPTER XIX 



PHYLUM XIII. STROBILOPHYTA 

 THE CONIFERS 



497. To a large extent this is a phylum of living plants, 

 and although many species and some genera have be- 

 come extinct, everj^ family is still represented in some part 

 of the world. The number of living species is about 400, 

 widely distributed throughout the earth. The Conifers 

 probably were derived from some of the old Cycads 

 {Cordaitales) to which they show some affinities. 



498. In these plants there is a still more marked 

 alternation of generations than in the preceding phyla. 

 The gametophytes are so minute and short-lived that 

 they are rarely seen, while the sporophytes are mostly 

 great trees with long-lived perennial roots and stems and 

 mostly perennial green leaves also. The phylum may be 

 defined as follows: Megaspores and microspores mostly 

 borne in homogeneous cones of sporophylls on the 

 arboreous sporophytes. Archegonial gametophytes very 

 minute, solid, ellipsoid, and permanent]}' enclosed in the 

 megaspore, which in turn is retained in the megasporan- 

 gium; antheridial gametophyte minute, few-celled, free, 

 developing a tubular antherid containing two noncili- 

 ated sperms. After the fertilization of the egg and the 

 formation of the cylindrical, leafy sporophyte, the 

 megasporangium, covered by an indusial coat (integu- 

 ment), becomes a ''seed." The sporophyte upon esca})ing 

 from the seed in germination grows into a perennial, 



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