174 Minnesota Plant Life. 



In a word, the most distinctive feature of the ferns is this: 

 They loosened that cone-arrangement of leaves which had arisen 

 in the club-mosses and greatly developed the spore-case-area 

 of each leaf until such an area became itself a leaf-like structure, 

 while the original blade of the leaf deteriorated and disappeared. 

 The pine trees, also related to the club-mosses, pursued a very 

 different course of development and retained the cone as a struc- 

 tural unit. From bodies somewhat similar to pine-cones it 

 is probable that the flowers of all higher plants arose. The 

 club-mosses then have originated two great lines of improve- 

 ment, one in which the cone was abandoned as a structural fea- 

 ture, giving rise to the ferns, the other, in which the cone was 

 retained as a structural feature, leading to the iJozvering plants. 



