68 OAK FERN. 



brighter green than almost any other British fern, 

 which, however, it is apt to lose if too much exposed 

 to the sun. The sori are borne on the margins of the 

 segments. 



This pretty and delicate fern occurs chiefly in wild 

 mountainous districts, wet woods, and the vicinity of 

 waterfalls, in our northern English, Welsh, and 

 Scotch counties. In Ireland it is a fern of great 

 rarity. Throughout Europe it is very generally 

 distributed. 



This is peculiarly a shade-loving fern. Besides the 

 delicate texture and graceful habit, the vivid green 

 hue of its foliage is its great attraction, and cannot be 

 preserved in exposed situations. Although a free 

 supply of moisture is recommended, care must be taken 

 that it does not remain stagnant, as it will speedily 

 destroy the plant by the decay of the rhizoma. By 

 care and attention to these facts, this beautiful little 

 fern will be found a pleasing and satisfactory addition 

 to a fernery. From its small size, it is well suited for 

 a fern-case. 



VARIETY. 



POLYPODIUM CALCAREUM (fig. 39), or the Limestone 

 Polypody (known also as Polypodium Robertiana), 

 appears to be merely a variety of the Oak Polypody, 

 of stouter growth, and occurring in limestone districts. 

 Its chief distinctions consist in the pinnate rather 

 than the ternate divisions of the fronds, which have a 

 glandular, mealy, or tubescent appearance. In de- 



