= 4) ae ‘ 
CHAPTER XII 
DIVISION PTERIDOPHYTA (FERNS AND FERN ALLIES) 
The pteridophytes are characterized by the alternation of two 
distinct kinds of plants: a gametophyte, or prothallus, which is a 
small thallus bearing archegonia or antheridia, or both (Fig. 432); 

Fig. 423. A group of large tree ferns (Cyathea) in a mountain forest in 
the Philippines 
‘and a sporophyte, which develops from the fertilized egg of a 
gametophyte and is differentiated into stems, roots, and leaves, 
and bears sporangia containing spores (Figs. 428, 424). On 
germination these spores give rise to the thallus gametophyte, 
or prothallus. 
385 
