Classification of Plants 



235 



Prothallium 



t 

 Spores 



Sporangium 



t 

 Fern Plant 



t 

 Oospore 



t t 

 Sperm cell Egg cell 



t t 



Antheridium Archegonium 



t t 

 Prothallium 



f 



I 



SPERMAPHYTA OR SEED-BEARING PLANTS. 



Although seed formation was given as a distinguishing 

 character of Spermaphyta, the nucellus of the ovule may be 

 compared to the megasporangium of Selaginella, where how- 



FIG. 209. Longitudinal section through an ovule of Pinus ready for 

 fertilization. /, testa showing middle hard layer ; n, nucellus. A micro- 

 spore has lodged within the micropyle and the pollen tube has nearly reached 

 the prothallium ; /, prothallium (endosperm) filling the macrosppre (embryo 

 sac). Two archegonia are seen at the micropylar end, one containing an egg 

 cell ; s, scale bearing the ovule. 



ever the spore output is still more reduced, as a rule in Sper- 

 maphyta only one megaspore of one spore mother-cell develops. 

 This was named the embryo sac before comparison revealed 

 the homology with the lower forms. 



