82 BRITISH PERNS. 



dantly northwards : and it also occurs on the Rocky Moun- 

 tains of the New World. It grows in very wet shady places 

 on the ledges of rocks. 



.CHAPTER XVH 



THE WOODSIAS. 



THE WootMas form a family group consisting of two di- 

 minutive kinds, which, however, possess much interest 

 among the British species on account _ of their extreme 

 rarity. These Ferns are furnished with indusia, and by the 

 peculiar construction and position of this organ, they may 

 readily be known. The peculiar nature of the indusia con- 

 sists in their being placed not as a cover to the sori, but at- 

 tached underneath them ; when very young they indeed en- 

 close them, but subsequently they split from above into 

 narrow scale-like segments not easily distinguished, without 

 optical assistance, from the hairs which occur along with 

 them on the fronds. In the full-grown state, the sori are 

 consequently seated in the centre of a spreading tuft of 

 hair-like scales, which are formed of the lacerated margins 

 of the indusium the latter being attached to the frond at 

 the point beneath the capsules. No other native Ferns pos- 

 sess a structure at all approaching to this. _ 



The name Woodsia was given in compliment to a veteran 

 English botanist, Joseph Woods, Esq., author of a very use- 

 ful Tourist's Flora. 



OBLONG WOODSIA. [Plate vm. left-hand fig.] 



This is the Woodsia ihemis._ It has been called Acrosti- 

 chum ilvense, and Polypodium ilvense. 



This Fern is a deciduous species, dying down to the 

 ground annually in winter, and reviving with the returning 

 spring. Its very short stems form _ tufted masses. The 

 fronds average about four inches in height, and are less fre- 

 quently found larger than smaller than this. Their, form is 

 lanceolate, more or less broad ; they are pinnate, 'che pinnaa 

 usually set on nearly or quite opposite in ^ pairs, and having 

 an obtusely oblong outline, with a cleeply-iobed or pinnatifid 

 margin. They are more or less clothed on both surfaces, but 

 especially on the veins beneath, with minute bristle-like 

 scales, and shining jointed hairs, among which the sori are 



