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 Fiowering 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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