Minnesota Plant Life. 



173 



has finally disappeared. In a family of tropical ferns not rep- 

 resented in Minnesota are found traces of this sterile segment 

 as stipular plates at the bases of the leaves. Therefore, we arrive 

 at the interesting and remarkable hypothesis that the entire 

 fern-leaf compares with a much elaborated and improved club- 

 moss spore-case. It will be remembered that the fertile seg- 

 ment of the adder's-tongue leaf was believed to be an over- 

 grown chambered spore-case arising from some club-moss-like 



FIG. 6(3. Maiden-hair ferns and lady ferns. After photograph by Williams. 



ancestral condition. Therefore, among true ferns the common 

 type of leaf in which both starch-making and spore-production 

 are combined, is the primitive one. By a division of labor, 

 some leaves quite abandoned the habit of producing spore-cases 

 and others in the same plant intermitted the production of leaf- 

 green. Thus are explained the two sorts of leaf in the ostrich- 

 fern and the same explanation serves for the cinnamon fern and 

 its allies and for the four-leaved water fern. 



