ALTERNATION OF GENERATIONS. 485 



prothallium; from one fertilized archegonium arises a Fern-plant with many fronls 

 and capable of producing millions of spores. Thus the species, whilst retaining to 

 itself such advantages as may be inherent in the sexual process, is likewise able 

 to diffuse itself in large numbers over an extended area by means of its numerous 

 asexually-produced spores. 



Allusion has been made to the advantages inherent in the sexual process. 

 The investigation of their precise nature will be one of the main problems reserved 

 for the second part of this volume. That a production of flowers and a ripening of 

 seed is not absolutely essential for the maintenance and distribution of plants, 

 seems not improbable judging from the considerable number of plants which do 

 well and flourish without them. 



