202 BOTANY. 
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. 
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Fia. 118.—Spore-case clusters (spore-dots, or sori) of various Ferns. .4, round 
and naked (Polypodium); B, round and covered (Aspidium); C, elongated and 
covered (Asplenium); D, elongated, and covered by folding of the leaf (Adian- 
tum). All magnified. (The covering is known as the indusium.) 
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 4 
