200 DERMAL AND OTHER NON-VASCULAR TISSUES [CH. 



with enlarged area of surface between the cells, results from this unusual 

 development. But the outer surface of the hair appears to be smooth, and 

 its form is cylindrical. 



In Trichonianes very characteristic hairs appear. Several stiff spines 

 radiate from a basal stalk. A similar condition is presented in Hymeno- 

 phyllum (Fig. 185, 4): in both of these genera the hairs may point in all 

 directions. But in some species of Polypodiwn and in Platyceriuvi the 

 branches radiate only in a plane parallel to the surface that bears them 

 (Fig. 188, I, 2). It is but a step from such stellate hairs to 2, peltate scale with 



I, 2. Stellate hairs oi Polypodiiim lingua. 3, 4. Peltate 

 scales of Polypoditim zncamim. ( x 65.) 



central attachment, such as is seen in Polypodhun incamini (Fig. 188, 3). By 

 stronger growth of the cells on one side of the scale the elongated form 

 characteristic of most of these protective scales is reached. Another way in 

 which protective scales are produced is by the repetition of longitudinal 

 divisions parallel to one another, while the hair in which they occur widens 

 into a flattened surface. The result in either case is that a flattened expansion 

 is formed, known as a I'amentiiin, common in the more advanced Leptospo- 

 rangiate Ferns (Fig. i88, 4). It is a particularly prominent feature in the 

 Cyatheae, distinguishing them sharply from the Dicksonieae, which have 

 only simple hairs. Frequently the distal cell, and sometimes marginal cells, 



