CHAPTER XX 



PHYLUM XIV. ANTHOPHYTA 

 FLOWERING PLANTS 



510. In this highest phylum we have the culmination 

 of the repeated structural advances in earlier phyla. 

 These plants are mainly modern, although some of the 

 more primitive forms originated as far back as the 

 Cretaceous period. It includes more than 132,000 known 

 species, that is, more than all the other phyla together. 



511. The Anthophyta probably were derived from the 

 Bennettitales among the Cycads. It is certain, at 

 any rate, that the flower structure of this ancient order 

 bears a remarkable resemblance to that of the lower orders 

 of the Flowering Plants. 



512. This phylum may be characterized summarily as 

 follows: Microspores and megaspores borne in flowers 

 on the leafy, rooted sporophytes. Flowers normally 

 consisting of more or less cone-like clusters of closed 

 megasporophylls (carpels) above, and microsporophylls 

 (stamens) below, and subtended by a perianth. Micro- 

 spores (pollen-cells) free at maturity, each producing a 

 one-celled gametophyte, and a tubular antherid, the 

 latter containing two non-ciliated sperms. Megaspore 

 retained within the megasporangium (ovule) where it 

 develops an egg in a reduced archegone and imma- 

 ture gametophyte. After fertilization the gametophyte 

 matures ("endosperm"), and the zygote develops into 

 a cylindrical, leafy sporophyte. The megasporangium 



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