FERTILIZATION, DEVELOPMENT, AND FRUCTIFICATION 



organs. They resemble seeds in that they are ex- 

 pelled from the parent-plant on attaining maturity, 

 and germinate on contact with the moist earth. 



Thus it is seen that the life-cycle of a fern consists 

 of two stages : 



First, the prothallium, bearing the reproductive 

 organs ; second, the fern-plant proper, developing 

 the spores which produce the prothallium. 



Along the moist, shaded banks of the wood road, 

 or on decaying stumps, keen eyes will discern fre- 

 quently the tiny green prothallia, although they are 

 somewhat difficult to find except in the green-house 

 where one can see them in abundance either in the 

 boxes used for growing the young plants, or on the 

 moist surfaces of flower-pots, where the spores have 

 fallen accidentally and have germinated. 



As the fertilization of the germ-cell in the arche- 

 gonium cannot take place except under water, per- 

 haps the fact is accounted for that ferns are found 

 chiefly in moist places. This water may be only a 

 sufficient amount of rain or dew to permit the anthe- 

 rozoids or fertilizing cells of the antheridium to 

 swim to the archegonium, which they enter for the 

 purpose of fertilizing the germ-cell. 



It is interesting to examine with a good magnify- 

 ing glass the sporangia borne on the lower surface 

 of a mature fertile frond. In many species each spo- 

 rangium or spore-case is surrounded with an elastic 

 ring, which at maturity contracts so suddenly as to 

 rupture the spore-case, and cause the expulsion of 

 the numberless spores (Fig. 7). 



35 



