Obviously, the only infallible way to discover this, is to cross the 

 supposed parents of suspected hybrids, and compare with the latter 

 the resultant plants. All other evidence regarding suspected hy- 

 brids, such as abortion or eccentricity of the fronds, sterility of the 

 spores, rarity of the plants, presence of the supposed parents, while 

 pointing to the almost irresistible conclusion that the fern is a hy- 

 brid, is not positive proof. I have found no record of any attempt 

 of the kind. American pteridologists appear to have left the hy- 

 bridizing of ferns to pteridologists abroad, who have confined their 

 attention to producing either entirely new forms, or new varieties 

 of the crested and laciniate ferns so dear to our English cousins. 



I am indebted to Mr. George E. Davenport's paper on " Hy- 

 bridity in Ferns," read before the Boston meeting of the Chapter, 

 not only for calling my attention to the subject, but also for sug- 

 gesting the experiments I have tried. In order to make clear a de- 

 scription of these experiments, it will be necessary for me to repeat 

 part of what he has already said. 



There are several methods by which the crossing of the sup- 

 posed parents of a suspected fern-hybrid may be attempted. As- 

 suming two species to be capable of blending, and their prothalli 

 monoecious, I will state briefly the possibilities of failure in each 

 method. 



The direct crossing of ferns by the artificial transference of an- 

 therozoids from one prothallus to the archegonium of another is 

 very difficult. I believe no one has succeeded in accomplishing it. 

 I have tried and failed. Owing to the infinitesimal size of the an- 

 therozoids, it must be done under a microscope and some instru- 

 ment must be devised that will lift the antherozoids not quiescent 

 and adhesive like pollen, but moving rapidly and deposit them 

 without injury upon the desired archegonium. 



Other, less direct, methods have proved more successful. The 

 simplest of these is to sow a mixture of the spores of the two ferns, 

 and trust to the proximity of the resultant prothalli to bring about 

 cross-fertilization. The disadvantages of this method are, that it is 

 impossible to tell whether the germinating spores come from both 

 species (which introduces an element of doubt into the final result), 

 that all or nearly all of one species may fail to germinate, and that, 

 in order not to lose a possible hybrid, it is necessary to raise every 

 one of the young plants, which means a great waste of time and 

 trouble. The objection may also be urged that even should both 

 species germinate, one might germinate later or develop faster than 



