8 



THE FERN BULLETIN 



down to the egg. About this time the antheridia 

 burst, liberating the sperms which by rapid motions of 

 their cilia swim through the dew-like moisture on 

 the gametophyte until they reach the archegonium, be- 

 ing attracted in that direction by malic and other acids 

 which it secretes. Arived at the archegonium the 

 sperms swim down through the neck and one at last 

 fuses with the egg thus forming the sexual spore from 

 which the new plant is to come. 



Although numerous archegonia are usually formed 

 on each gametophyte various conditions combine to 

 prevent the fertilization of more than one egg and in 

 consequence the gametophyte rarely produces more 

 than a single fern-plant. It is interesting to note that 

 while the sex-organs are normally borne on the under- 

 side of the gametophyte, this appears to be due 

 largely to the light for if the gametophyte be brightly 

 illuminated from below, it will produce the sex-organs 

 on the darker upper surface. 



A thorough understanding of the processes that 

 lead up to the formation of the sexual spore is neces- 

 sary for the intelligent hybridizing of ferns. The only 

 way that two different species can be crossed is by 

 causing the sperm of one to unite with the eggs of an- 

 other. A chance cross may result when the spores of 

 two different kinds are sown thickly together but the 

 crossing may be brought about more certainly by sect- 

 ioning the prothallia with a sharp knife in such a way 

 that each piece shall have but a single kind of sex- 

 organ upon it. Then, by planting a section of one 

 with archegonia close to another with antheridia, a 

 cross is practically certain. The only difficulty in the 

 way is the small size of the prothallia which makes 

 proper sectioning a delicate matter. All natural hy- 



