10 PERNS OF GEEAT BRITAIN. 



time the outer thin skin or cuticle of the leaf above these 

 stripes separates a little from the green part; then it 

 becomes raised by their growth, the raised part assuming 

 the form of the little heap of capsules beneath ; tiU finally 

 these burst through the skin, and separate it into two 

 equal parts, one edge of which remains adhering to the 

 leaf. This thin skin is the indusium. This frequently 

 disappears before the seeds are ripened. Though usually 

 of the same form as the cluster, it is not always so, but 

 in some few of our native species, as in the Filmy Perns, 

 it is cup-shaped, and it is then often called an involucre. 

 The spores of ferns are very numerous, exceedingly 

 minute, and of an oval form. 



The frond of the fern arises from the rhizoma or root- 

 stock, which may be generally described as a creeping 

 underground or horizontal stem, though in some exotic 

 species it rises erect, and emerging from the earth, 

 resembles the shaggy trunk of a palm. The rhizoma of 

 our native ferns is usually covered with shaggy scales 

 or hairs, which sometimes, as in the Common Brake, 

 are so fine and numerous, that they form a surface 

 of velvety down. Sometimes this rhizoma sends out so 

 many shoots, that they form a firm network beneath the 

 surface of the soil ; but more often this portion of the 

 fern occupies httle space in the ground. Some root- 

 stocks of ferns are of a deep, rich, red-brown hue. A very 

 common species in our conservatories, the Hare's-foot 

 Fern {BavcUlia Canariensis) — which, as its name implies, 

 has been introduced from that region of beautiful plants, 

 the Canary Islands — has dark shaggy masses of root- 

 slock abo\it the base of its frond, which terminate in a 



