256 



THE SENSITIVE AND OSTRICH FERNS. 



where this author obtained his specimens. In the fourth 

 edition of Amos Eaton's botany published in 1834, the 

 author says : " The leaflets slowly ap- 

 proach each other on squeezing the stem 

 in the hand." Many observers will testify 

 that they cannot be made to do so in these 

 degenerate days. The species is some- 

 times called oak fern or oak-leaved fern. 

 In some ancient botanical works it is 

 mentioned as " dragon's bridges," though 

 for what reason, no one seems to know. 

 The sensitive fern is abundant in nearly 

 all the territory from Canada to the Gulf 

 of Mexico and west to the Mississippi. 

 Scattered colonies occur as far west as 

 Wyoming, and the same species is again noticed in 

 Japan. In Montana, this species, or one exceed- 

 ingly like it, has been found as a fossil. 



Growing with normal fronds, there is often 

 found a form half-way between fertile and sterile. 

 It was once considered to be a permanent type 

 and given the varietal name of obtusilobata, but it 

 is now known to be due merely to the destruction 

 of the early sterile fronds. It usually contains 

 less leaf surface than the ordinary sterile frond 

 and in cutting resembles the twice pinnate fertile 

 one. Commonly it bears a few abortive sori, all 

 of which show it to be a partially transformed 

 fertile frond. Prof. Geo. F. Atkinson, who made 

 extensive experiments with this plant, found 

 that he was able to produce the variety at will, by 

 *^ cutting off the early sterile fronds. 



obtusilobata. 



