420 



THE VASCULAR PLANTS 



Fig. 211. — Shows the method by which 

 the sporangium, by means o( its an- 

 nulus, discharges the spores. 



ture is produced by a spore, it is, of course, a gametophyte. 



The prbthallia of true ferns are small, heart-shaped, flat, 



green bodies. (See Figure 

 212.) They produce their 

 archegonia and antheridia 

 on the under surface. (See 

 Figure 213.) The sperms 

 of pteridophytes are larger 

 than those of bryophytes 

 and have many cilia. The 

 archegonia have short necks 

 and their venters are em- 

 bedded. (See Figure 214.) 

 After fertihzation, the 

 sporophyte (the fern plant) 

 grows out of the archego- 



nium and up from the prothallium, the first leaf usually 



appearing just above the notch of the heart. Where very 



young ferns are found you may often 



find prothallia either still attached to 



them, or without the sporophyte yet 



showing. (See Figure 212.) Pro- 

 thallia are often found on damp brick 



walls and on flower pots in old green- 

 houses in which ferns are grown. 

 The growth of new fern leaves 



from their underground stems is 



more conspicuous than their growth 



from prothallia, and when ferns are 



planted in yards or gardens the 



underground stems are used. They 



send up new fronds each season 



^-'Wsv'CS^ 



Fig. 212. — Prothallia (ga- 

 metophytes) of a true 

 fern. A, prothalUum 

 with a young sporophyte 

 arising from it. B, a 

 group of prothallia with- 

 out sporophytes. 



(see page 156). 



