222 THE CHAIN FERNS. 



only to the sterile fronds. Since both the sensitive fern 

 and the chain fern fruit late in the year, there is a large 

 part of the season when they are easily confused, espe- 

 cially if the collector has never seen both growing. It is 

 not to be inferred, however, that it is impossible, or even 

 difficult, to separate the species when sterile. When 

 they are in fruit there is, of course, no chance of mis- 

 taking them. 



The rootstock is quite slender and creeping and the 

 fronds somewhat scattered along it. The sterile are 

 twelve to twenty inches long with slender, straw-coloured 

 stipes and ovate blades cut nearly to the midrib into 

 oblong, acute lobes. Toward the base, the lobes incline 

 to be separate, the part nearest the rachis being rapidly 

 narrowed into a broadly winged stalk. This makes the 

 blade appear pinnate, at least at base, but there is usually 

 a narrow wing of membrane connecting even the lowest 

 division with the rest. All the pinnules are finely ser- 

 rate on the edges. 



In June the taller fertile fronds begin to come up. 

 They are on longer stipes and quite unlike the sterile 

 fronds. Even the stipe is of a different colour, being 

 black and polished, while the blade is distinctly pinnate 

 with long, narrowly-linear, distant pinnules that seem 

 just wide enough to hold the two lines of large, heavy, 

 sunken sori. None of our other ferns have an indusium 

 so thick and corky, and perhaps for this reason the fer- 

 tile fronds are much heavier than the sterile. Long 

 after its usefulness has departed, this indusium remains 

 attached to the frond. There are many curious grada- 

 tions between fertile and sterile fronds both in the shape 

 of the pinnules and in fruitfulness. In the northern 

 part of its range, at least, this species is not evergreen 



