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. Diagrammatic representation of the life history of the fern: (a) prothallium; 

 (b r ) antheridium; (6") archegonium; (c'i sperm; (c") ovum; (d) oospore; (e) prothallus and 

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

 rangium; (h) spores. 



spots which vary in size and shape dependent on the species. 

 They are known as sori (singular, sorus) 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- 



