GERMINATION OF FERN SPORES. 



21 



inent than the antheridia, consisting of an external layer of 

 cells and a large central cell, which soon divides into two. The 

 lower portion, at first the larger, develops into a roundish cell, 

 which is analogous to the ovule of flowering plants, and is called 

 the oosphere. The upper portion of the central cell develops 

 between those composing the neck of the archegonium into a 

 canal filled with a sort of mucilage ; this finally swells up, forces 

 the cells of the neck apart, and is expelled to aid in attracting 



FIG. 14. Antheridium of Adiantum FIG. 15. Young archegonium of Pteris 

 capillus-veneris L., showing the es- serrulata Linn, f., showing oosphere, 

 caping antherozoids. (After Sachs.) neck, and canal-cell. (After Sachs.) 



and retaining the antherozoids at the neck of the archegonium. 

 The oosphere is thus left exposed (Fig. 15). 



65. Fertilization. The antherozoids, analogous to the 

 pollen of flowers, when discharged from the antheridium swim 

 in the moisture always present on the under surface of the 

 prothallium, swarm in large numbers around the neck of the 

 archegonium, and are retained by the mucilage. Some finally 

 force their way into the canal of the neck, a few reaching the 

 oosphere and disappearing within its substance. There is thus 

 a true sexual generation among ferns, and the formerly appro- 

 priate term Cryptogamia (hidden marriage) loses its application 

 under the untiring scrutiny of the microscopist. After fertili- 

 zation the neck of the archegonium closes, and the fertilized 



