38 ON THE STRUCTURE AND 



polypody and the spleen-wort they attain a consider- 

 able size. When out of the ground, they are covered 

 with scales and hairs, and present a very shaggy ap- 

 pearance. In some cases, as in the common brakes 

 and the Flowery Fern, the stem rises erect in the air, 

 and bears its fronds in the same way as higher plants 

 bear their leaves. It is "in tropical ferns that these 

 stems attain their greatest size, and rise above the 

 ground forty or fifty feet in height. Such ferns are 

 called tree-ferns. But the nature of this stem is the 

 same in all cases : it consists of a mixture of woody 

 and cellular tissue, constituting the basis of the 

 fronds ; and in cases where the stem is perennial, it 

 consists ot the remains ot the successive annual 

 developments of the fronds. 



The fronds vary much in form, and the stalk on 

 which they are placed is called the stipes. They vary 

 in size, and also in duration : they usually, how- 

 ever, come up in the spring, and die down in the 

 autumn. 



The frond, like the leaf, is divided into the blade 

 and stalk, or stipes. The woody tissue ot which the 

 stipes is formed is continued into the blade, and con- 

 stitutes there the veins or ribs. The middle portion, 

 which runs up the whole frond, is called the midrib. 



The same terms are applied to the shape of the 

 frond as to the leaf. When the blade is undivided, as 

 in the Hart's-tongue, it is called entire ; when the 

 frond is scalloped out, and the indentations do not 

 reach the midrib, the frond is said to be pinnatifid ; 

 when the indentations reach the midrib, and leave a 

 series of little leaflets, or pinnce, the frond is said to 

 be pinnated. The pinnce may be again divided down 

 to their veins or ribs, and the frond is then said to be 

 twice-cut, or bi-pinnate. When this occurs a third 

 time, it is tri-pinnate ; and when oftener, the frond is 

 said to be decompound. This latter does not, however, 



