THE BLADDER FERNS. 77 



soil for it is very light turfy peat, mixed with a considerable 

 proportion of silver sand, and it is beneficial to plant it on 

 or around a small lump of free sandstone. 



CHAPTER XVI. 



THE BLADDER FERNS. 



THE botanical name of this group is Cystopteris. The 

 species of Cystopteris are all small, fragile Ferns, yet, not- 

 withstanding, they are very beautiful and very interesting. 

 They are much more delicate and herbaceous in their texture 

 than the majority of our native species, and hence are well 

 adapted for the purpose of minute investigation into the 

 nature of their venation and fructification. Their texture 

 alone almost suffices to tell a practised eye their family posi- 

 tion, but the tyro needs a more precise characteristic, and 

 this is found in the structure of the scale or indusium which 

 covers the sori. The sori of these plants are round, as in 

 Lastrea and Polystichum, all, equally with _ Cystopteris, once 

 included under the old family name of Aspldium ; but here, 

 instead of being almost flat and circular, the cover is inflated 

 or bulged out like a hood, and is attached at the back (to- 

 wards the base of the pinnule) of the sorus by its broad base, 

 covering the spore-cases while in a young state, but becom- 

 ing ultimately reflexed at the point, which is more or less 

 jagged or fringed. Hence these plants are called Bladder 

 Ferns. There are three native species, of one of which 

 numerous distinct forms or varieties occur. 



The technical name comes from two Greek words, which 

 respectively mean bladder and fern ; so that in this case the 

 English appellation is a literal translation of the scientific 

 name. 



BRITTLE BLADDER FERN, [Plate X. fig. 2.] 



This Fern, generally known among botanists as Cystopteris 

 fragilis, has a host of other names. Some of these are 

 Cyathea fragilis, C. cynapifolia, C. anthriscifolia, C. dentata; 

 Cystea fragilis, C. angustata, C. dentata ; Polypodium fra- 

 gile, P. cynapifolium, P. anthriscifolium, P. dentatum. P. 

 rhoeticum; Aspidium fragile, A. dentatum, and A. rhceticum. 



The Brittle Bladder Fern is a tufted-growing plant, 

 spreading, if undisturbed under congenial circumstances, 



