Chapter XVIII. 



Ferns and Water-ferns. 



Related to clnlj-mosses in about the same manner that true 

 mosses are related to horned liverworts are the ferns, a very 

 ancient and singular group of plants. In Minnesota about fifty 

 species occur, found for the most part in woodland. One va- 

 riety, the brake, is an exceedingly common plant in all burned 

 districts of the forest region. 



Adder's-tongues and moonworts. There are two principal 

 groups of ferns recognized by botanists. Of the lower group, 

 the so-called grape-ferns or moonworts and the adder's-tongue 

 ferns are specimens. In these each leaf consists of two lobes, 

 one — the so called sterile lobe — being devoted entirely to 

 starch-making, the other — the so called fertile lobe — having for 

 its exclusive function the production of spore-cases. The fer- 

 tile lobe grows from the inner face of the sterile lobe, occupy- 

 ing relatively to the sterile lobe the same position maintained by 

 the spore-case of a club-moss with reference to the leaf upon 

 which it was situated. It is believed that the fertile lobe of an 

 adder's-tongue fern-leaf is equivalent to a large, chambered and 

 overgrown spore-case as displayed in the club-mosses, and it is 

 believed that the sterile segment of the leaf is equivalent to the 

 blade of the spore-case-bearing leaf in the club-mosses. 



The adder's-tongue ferns with their slender fertile lobes bear- 

 ing two rows of spore-cases and their undivided sterile seg- 

 ments, are simpler than the grape-ferns with their palmately 

 branched leaf-segments. In these plants the spores upon germ- 

 ination give rise to little tuberous sexual plants which lie almost 

 imbedded in the soil and are devoid of leaf-green, being humus 

 plants. Upon such little tubers the egg-organs and spermaries 

 develop and after fecundation the egg forms an embryo which 

 nurses for a time upon the sexual plant, then thrusts its own 



12 



