PTERIDOPHYTES 



299 



Stem, but they are made up of tissues ■which are the same or 

 similar tO' those of the Spermatophytes. 



The leaves (or fronds) (Figs. 144, 145, 146, 147, 148, 149) 

 have a structure very similar to< that of the Spermatophytes. 

 On the backs of the fronds will be found characteristic brown 



Fig. 144. — Diagranunatic representation of the life history of the fern: (a) prothallium; 

 (&') antheridium; (6") archegonium ; (c'J sperm; (c") ovum; id) oospore; Ce) prothallus and 

 young fern; (/) mature fern showing underground stem, root and leaf-bearing sori; ig) spo- 

 rangium; i.h) spores. 



spO'ts which* vary in size and shape dependent on the species. 

 They are known as sori (singular, sonis) and in most species are 

 covered -with very thin membranes known as indusia (singular, 

 indusium). These sori are composed of sporangia, which in the 

 typical ferns are stalked bodies. They can be readily repre- 

 sented by two watch glasses placed with their concave sides to- 



