492 General Botany 



among the lycopods, and has occurred among the equisetums 

 that are now extinct. 



Gametophytes. Both the male and female gametophytes 

 are small or microscopic, being formed partly or wholly inside 

 the spore wall. Here, then, are the most-reduced gametophytes 

 among the Pteridophytes. 



Seeds. Before leaving the Pteridophytes, attention should 

 be called to the fact that occasionally the large spores of Selagi- 

 nella germinate within the sporangium and produce a prothallus. 

 Fertilization may take place, followed by the development of an 

 embryo sporophyte before the megaspore leaves the megasporan- 

 gium. These are rare and accidental happenings in Selaginella, 

 but when they occur we have the same arrangement of struc- 

 tures that regularly occurs in the formation of the seeds in sper- 

 matophytes. A seed is the result of telescoping a gametophyte 

 and a new sporophyte within a sporangium : 



Fig. 3C5. Selaginella martensii, showing leaf -like shoots with cones at the ends of the 



smaller branches. 



