FERNS OP GREAT BRITAIN. 9 



tongue found on pasture-lands, are instances of this 

 form of fructification. 



The small patches on the backs of fern-leaves are 

 the sori, or clusters of capsules. These capsules are 

 sometimes termed spore-cases, or sporangia, or thecce, 

 and they contain the spores, which are analogous in 

 their uses to the seeds of flowering-plants, though 

 differing from them in their origin as well as struc- 

 ture. They are a mass of cellular substance, without 

 cotyledons ; and instead of sending a shoot up into the 

 air and radical fibres downwards, as the seeds of flower- 

 ing plants do, they germinate indifferently from any part 

 of the surface. The capsules, as seen under a micro- 

 scope, are beautiful objects, resembling little hollow 

 spheres of crystal, tinged with a delicate brown hue, and 

 are discovered in most cases to consist of one cell, and 

 to be surrounded by a jointed elastic ring, and to be sup- 

 ported below on an exquisitely slender stalk. When the 

 spores are fully matured, the elastic nature of this ring 

 causes various quick movements, by which the spores or 

 fern-seeds, which look like fine dust, are jerked from the 

 capsule. In some plants, as in the Flowering Fern, the 

 Moonwort, and the Adder's-tongue, the seed-cases are 

 destitute of the elastic ring, and are two-valved. 



These clusters of spore-cases are sometimes formed 

 outside the skin of the leaf, and are without covering ; 

 but in most of our native ferns, especially during their 

 early growth, they axe covered by a thin membrane 

 called the indusium. If we examine a young fern, we 

 see first a number of little pale-coloured stripes appearing 

 at equal distances upon some of the veins. In a short 



c 



