42 BRITISH FERNS 



containing erratic and indefinitely varied forms, and that the best 

 plan is to select two, and only two, quite distinct varieties, whose 

 character may be clearly distinguished if a cross occurs. Owing 

 to the practical impossibility of securing a cross by hand, as is 

 easily done with flowers, it is only by such selection that practical 

 certainty can be eventually secured. 



