202 



BoTANT. 



sides. They are among the most beautiful of our land- 

 plants, and their leaves furnish examples of a gracefulness 

 of bearing and outline scarcely excelled in the vegetable 

 kingdom. In temperate climates ferns are herbaceous, but 

 in the tropics many possess a perennial woody stem which 

 bears a crown of leaves upon its summit. 



425. The tissues of the True Ferns are well developed. 

 The epidermis resembles that of the flowering plants. 



Fio. 113.— Spore-case clusters (spoie-dots, or sori) oE various Ferns. A, round 

 and naked (Polypodium); B, round and covered (Aspidium); C, elongated and 

 covered (A splenlum); i>, elongated, and covei-ed by folding of the leaf (Adian- 

 turn). All magnified. (The covering is known as the induslum.) 



Complicated fibro-vascular bundles run through the stems 

 and extend into the leaves, where they branch extensively, 

 forming the delicate veins which are so characteristic of 

 fern-leaves. 



426. The young leaves before expanding are coiled or 

 rolled, so that as they grow up and open they unroll from 

 below upwards (i.e., circinately). Upon the lower surface 

 of some of the leaves little clusters of club-shaped hairs 

 (trichomes) grow out, generally in connection with a fibro- 

 vascular bundle. The internal cells of the larger end of 

 these hairs undergo subdivision, and thus give rise to a 



