FUNCTIONS OF FERNS. 89 



often occur in British species. The more vigorous 

 specimens of the Common Brakes occasionally pre- 

 sent it. 



When the fronds are first formed in the bud, they 

 are rolled up in a peculiar way. The whole frond is 

 rolled up from the point to the base, upon itself ; and 

 when it is divided into pinnse, each pinna is rolled in 

 the same way upon itself. This arrangement occurs 

 in other plants, and is called circinate. All British 

 ferns, with the exception of the AdderVtongue and 

 Moonwort, have this circinate arrangement of their 

 fronds. 



The veins or ribs of the fronds are variously ar- 

 ranged, forming sometimes good characters for the 

 distinction of species. These veins are never netted, as 

 they are in the majority oi flowering plants, but they 

 are often forked, or dichotomous. It is upon the 

 veins of the under-part of the frond that the oi-gans 

 ot fructification are placed ; and this part is called the 

 receptacle. 



The organs of fructification consist of a number of 

 little capsules, called seed-cases, spore-cases, sporangia, 

 or thecae. These are collected together in little 

 clusters, which are called sori. The sori are placed 

 upon the receptacle. When the sori are placed on 

 the under-part of the frond, they are called dorsal ; 

 but when on the edge of the frond, marginal. They 

 are never placed on the upper surface of the frond 

 alone. Sometimes the whole frond is converted into a 

 receptacle, as in the case of the Flowering Fern, the 

 AdderVtongue, and some others. 



The spore-cases are mostly small, slightly ovate 

 bodies, with a single cavity. They are surrounded 

 with a ring, one end of which is fixed to the recep- 

 tacle. When the spores contained in the inside have 

 reached maturity, the elasticity of the ring causes the 

 spore-case to burst transversely, and the spores are 



