CHAPTER FORTY-SIX 



GYMNOSPERMS: THE CYCADS 



The term gymnosperm (naked seed) is applied to those plants 

 whose seeds are attached to a sporophyll, but are not inclosed 

 in an ovulary. Attention, was called in an earlier chapter (page 

 492) to the fact that a Selaginella may occasionally form a struc- 

 ture which could not be excluded from any definition of a seed. 

 Furthermore, it is definitely known that some of the ancestral 

 lycopods attained the seed habit in Paleozoic times. The 

 cordaites formed a second group of Paleozoic seed plants. At 

 the same time there were plants, Pteridosperms, so closely re- 

 sembling ferns that, until the rather recent discovery of seeds 

 attached to their leaves, they were classified as ferns. From 

 the seed ferns came the Mesozoic cycads (Bennettitales), having 

 thick tuberous stems with a crown of foliage leaves superficially 

 like some of the modern cycads. All these forms were gymno- 

 sperms, and attention is directed to them again merely to em- 

 phasize the fact that the record of the transition from Pterido- 

 phytes to gymnosperms is remarkably complete, and that seeds 

 arose in several quite independent phyla of plants. 



The cycads. Of the living gymnosperms the most primitive 

 are the cycads. This interesting group of seed plants with fern- 

 like leaves and stems and many other characteristics reminiscent 

 of their fern-like ancestors is practically confined to tropical and 

 subtropical regions. There are about 100 species belonging to 

 nine genera, of which five occur only in the eastern hemisphere 

 and four only in the western. Specimens of several species 

 are common in conservatories, among them the " sago palm " 

 (Cycas revoluta). The graceful, rigid leaves of this species are 

 frequently seen in floral decorations and on Palm Sunday. 



The cycad sporophyte. The cycad stem is either an under- 

 ground erect tuberous body, or a columnar trunk 5 to 60 feet in 

 height. The columnar stems are covered with an armor of old 

 leaf bases like that of certain tree ferns and of the fossil cycads. 



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