IX FILICINEAi LllPTOSPORANGIAT^ 335 



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Upon the upper surface. Usually, but not always, the devel- 

 opment of the young stoma is preceded by the formation of a 

 preliminary cell (Fig. 185, t'), horse-shoe shaped, and cut- 

 ting off a small cell from one corner of an epidermal cell. A 

 similar wall forms within this small cell, parallel to the first 

 one (Fig. 185, B, st), and the cell thus separated is the stoma 

 mother cell. A longitudinal wall next divides this, and then 

 splits in the middle to form the pore of the stoma (Fig. 185, 

 C). This when complete is exactly in structure tike those of 

 other vascular plants, and like them communicates with the air- 

 spaces of the mesophyll. The accessory cell enlarges very 

 much with the expansion of the leaf, and its w^alls have the same 

 sinuous outline that the other epidermal cells exhibit. A curi- 

 ous variation of the ordinary form is seen in Anciinia (De 

 Bary (3), p. 42), where the mother cell of the stoma is cut out 

 by a perfectly circular wall, very much like the funnel-shaped 

 one in the antheridium, and the stoma is apparently free in 

 the centre of an epidermal cell. It seems that this also occurs 

 in Polypodhiin lingua (De Bary, 1. c). 



Most of the Leptosporangiatse are characterised by numer- 

 ous epidermal outgrow'ths, either hairs or scales. These are 

 especially abundant upon the younger parts, and are largely 

 protective. The hairs are either simple or glandular ones. In 

 the latter case the gland is usually a terminal, pear-shaped cell, 

 wdiich secretes mucilaginous matter, or less frequently (Onoclca 

 struthioptcris) this secretion may be resinous. In the common 

 Californian ''gold-back" Fern, Gyinno gramme triangularis, the 

 yellow powder upon the back of the leaf is a w^axy secretion, 

 derived from epidermal hairs. Of similar nature are the large 

 chafify scales (pale?e) which occur in such numbers upon the 

 bases of the petioles of so many Ferns. This development of 

 hairs, however, is most marked in the large tree-Ferns, Dick- 

 sonia, Cibofiiim, etc., wdiere the young leaves are completely 

 buried in a thick mass of brown wool-like hairs, wdiich are 

 sometimes utilised as a substitute for wool in stuffing mat- 

 tresses, etc. 



The Root 



The roots arise in large numbers in most Ferns, and appar- 

 ently bear no definite relation to the leaves. The primary ones 

 are first visible very near the apex of the stem (Fig. 181, A, r), 



