108 



THE FERN BULLETIN 



will show several sori in each close-wrapped pinnule, 

 each sorus, surrounded by its own hood-shaped indus- 

 ium. 



The fertile and sterile fronds are also widely separ- 

 ated as regards the time of appearance and it may be 

 doubted whether there is anywhere another fern that 

 excels it in this respect. There are various other di- 

 morphic species in our fern flora, but in these the two 

 kinds of fronds usually appear without much time 

 elapsing between them. In the cinnamon fern (Os- 

 munda cinnamomea) , they appear almost simultan- 

 eously, but in the species under discussion the fertile 

 fronds often do not appear until August or even later. 

 It is thus seen that this forms an ideal species for ex- 

 perimentation in the production of abnormal forms. 



The typical obtusilobata fronds are about half way 

 between the fertile and sterile fronds in appearance, 

 but a complete set of intergrading forms from the per- 

 fectly sterile to the completely fertile may be found. 

 It was once thought that the obtusilobata forms were 

 sterile, but careful search on the backs of the fronds 

 will usually reveal certain whitish scales which are the 

 indusia of imperfect sori. In some cases, also, small 

 prothallia instead of spore-cases have been found in 

 such sori, adding this species to the list of ferns known 

 to exhibit apospory. 



When first discovered the obtusilobata forms were 

 regarded as sterile fronds that had in some way taken 

 on the additional function of spore-bearing. L. M. 

 Underwood appears to have been the first to suggest 

 that the real condition is just the other way 

 about and that the forms are all transformed from 

 what the plant intended originally for fertile 

 fronds. For a time a considerable controversy 



