1 68 



Minnesota Plant Life, 



Four-leaved water-fern. 

 Brown. 



After Britton and 



an embryo which sucks 

 up all the surplus food- 

 materials that were de- 

 posited in the large- 

 spore, produces a root of 

 its own, thrusts it into the 

 soil or water and begins 

 an independent existence. 

 The Minnesota variety is 

 a land-dwelling species of 

 a group which is more 

 generally aquatic, hence 

 the name of water-fern. 



The fusion of the egg 

 and the sperm in ferns can 

 take place only after heavy 

 rains, or when the melt- 

 ing snows of early springs FlG - 

 have flooded the station 

 of the plant. All ferns, and indeed, most plants, up to and includ- 

 ing the cycad-palms and ginkgo trees, are essentially aquatic in 



their breeding hab- 

 its. Most of them 

 have motile sperms 

 provided with swim- 

 ming hairs, and un- 

 less there is a me- 

 dium in which the 

 sperm can swim it 

 will never reach the 



egg- 



Floating ferns. 



The family of the 

 floating ferns is rep- 

 resented in Minne- 

 sota by a little plant 

 called A zolla, not un- 



FIG. 60. A sexual fern-plant somewhat magnified. Its nat- COmmon m greeil- 



ural size is about a quarter of an inch across. The round h O U S C S where it 



bodies are spermaries, the chimney-shaped ones are egg- ,, 



organs, seen from below. After Atkinson. floats UpOll the SU1~- 



