84 FERNSTHEIR NATURE AND CLASSES [CH. 



30 feet, like a palm. I have seen the stem of our Royal 

 Fern (Osmunda} rising more than 12 inches, after the 

 manner of the Tree Ferns ; and the Male Fern (Filix- 

 mas), when undisturbed for years, sometimes grows as 

 high ; but these cases are exceptional. 



The stem is sometimes called a rhizome, when it 

 creeps horizontally on or beneath the surface and from 

 it the fibrous roots strike down or adhere to the rock or 

 branch. These rhizomes when on the surface are covered 

 with hairs or scales ; of this habit the Polypodies are the 

 most familiar examples. 



The leaves of Ferns known as fronds are something 

 between a stem and a leaf in an ordinary plant ; they 

 are endless in their variety, some immense, others minute, 

 some simple, others divided and sub-divided, some soon 

 fade, others are practically evergreens. 



The fronds are traversed by veins running either in 

 parallel lines or in networks, the way in which these 

 veins are disposed is termed their venation, and the 

 nature of this venation indicates the divisions of the 

 ferns into family groups. It is from these veins that the 

 clusters of spore-cases are derived, and each separate 

 cluster of these cases is called by botanists a sorus. 



Without going into the question of the botanical 

 classification of Ferns, it may be well to suggest that our 

 British Ferns may be roughly classed under two groups. 

 The first, a small family, whose spore-cases not being 

 surrounded by a ring (annulus), are called exannulate. 

 They are Adder's Tongue, Moonworts, Osmunda. As in 



