CH. XIII] 



THE CYCADS 



517 



the Angiosperms. Phylogenetically they are closely related 

 to the Pteridophytes. While nearest to Selaginellas among 

 living forms, especially as to their reproduction, the evi- 

 dence of palaeontology shows that our Gymnosperms are 

 descended from ancient Fern-like forms through the inter- 

 mediate group of extinct plants called Pteridosperms ("seed 

 ferns") or Cycadofilicales. Apparently our existent Gym- 

 nosperms are a survival of those which, the first to develop 

 the pollen tube, were able to occupy drier situations upon 

 the earth than were possible to the true Pteridophytes, with 

 their need for keeping a prothallus upon wet ground. Thus 

 we can imagine a time when the forests of the earth consisted 

 of Pteridophytes in the moister places, with Gymnosperms 

 in those which were drier, though now both groups have 

 been largely displaced in both situations by the Angiosperms. 

 The Gymnosperms include three leading Orders, 



ORDER 1. CYCADALES: THE CYCADS. 

 ORDER 2. CONIFERALES : THE CONIFERS. 

 ORDER 3. GNETALES : THE GNETUMS AND KIN. 



ORDER 1. CYCADALES: THE CYCADS. These are woody 

 plants of warm regions, mostly with slow-growing unbranched 

 trunks bearing a crown of 

 very stiff pinnately-cona- 

 pound leaves. Some 80 

 species are known. 



The most familiar form 

 is Cycas revoluta, or Sago 

 Palm (Fig. 363), from 

 eastern Asia, grown in 

 large conservatories partly 

 for ornament and partly 

 for its leaves, which are 

 much used in funeral dec- 

 orations. Its rough Colum- FlG - 363.-Ci^fl revoluta, x; as 



commonly seen in our greenhouses. 



nar trunk reaches some (From Bailey.) 



