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A TEXTBOOK OF BOTANY 



[Ch. XII 



and is green, and thus is an independent plant. On its 

 under surface it bears archegonia, which are flask-shaped 

 bodies containing each an egg cell, much like those of Bryo- 

 phytes but shorter and partly sunken in the prothallus; 

 while the antheridia are compact structures developed 



Fig. 351. — The life cycle of a Fern, chiefly Aspidium species. 



Left, the plant; X tV Right, above, a pinna showing sori; X 2- Sec- 

 ond line, a sorus, showing indusium and sporangia, X 10 ; a sporangium, 

 X 50, with a single spore (below, left), X 100. Next a prothallus, seen from 

 below, showing the spore, rhizoids, archegonia and antheridia, X 3, with a 

 median section below, X 6. Lower line, antheridium expelling sperm cells, 

 X 120, and a single sperm cell, with still-attached lining of mother cell, 

 X 300 ; ripe open archegonium, with sperm cell in neck, X 120 ; and young 

 Fern developing from fertilized egg-cell. (In part from nature, and in 

 part after L. Kny.) 



on the surface. In these are formed the sperm cells, which 

 are spiral and multi-ciliate, and carry for a time the sac-like 

 lining of their mother cell. On access of water the 

 antheridia swell and expel the sperm cells, while the arche- 

 gonia exude a substance, i.e. malic acid, very attractive to 

 them. Accordingly, they swim into the open neck of the 



