THE PTERIDOPHYTA : FILICALES, THE FERNS 



533 



The meduUated, monostelic, vascular structure of the stem. 

 The absence of distinct sori and of indusia. 



The irregularity of the divisions at the early stages of sporangial 

 development. 



6. The large sporangia, with no proper annulus and with a relatively 



large spore output. 



7. The massive and long-lived prothallus. 



8. The complex wall system and large size of the antheridia. 



9. The slow development of organs in the embryo. 



Eusporangiatae : Marattiaceae 



The Marattiaceae are distinguished by the massive sporangia which 

 originate from a group of cells, not from a single cell, as in the Lepto- 

 sporangiatae. They are correspondingly robust in all their parts ; the 

 stems are solid and almost tuberous, the petioles thick and long, and the 

 leaves large and leathery. 



^ Marattia fraxinea 



Species of Marattia are very large Ferns, native to both Eastern and 

 Western Tropics, and often cultivated as hothouse plants (Fig. 530). 



Fig. 530. — Marattia fraxinea. Plant growing at Kew 

 Gardens. Much reduced. 



Marattia fraxinea is one of the most widely distributed species, occurring as 

 far south as New Zealand. 



The stem is about 10 cm. high and the same in thickness. The petioles 

 are about 50 cm. long and 2 to 3 cm. thick. The leaf blade may be a square 



