XI] 



HAIRS AND SCALES 



also are glandular (Fig, 189). This, together with the whole structure and 



development, indicates that the scale is derivative from the simple hair. Such 



scales overlapping closely form a very perfect covering to the surface that 



bears them. The protection may 



be permanent in Ferns exposed C^i 



to drought, such as the whole plant 



of Polypodium incamim ; or they 



may be restricted to the rhizome, 



as \x\Phleb odium aureum ( Fig. 1 90). 



They may fall away in the adult 



after having protected the parts 



while young, as xnDryopterisFilix- 



inas. 



In some families of Ferns the 

 difference between simple hairs 

 and scales may be used to con- 

 firm a distinction between primi- 

 tive and derivative genera, based 

 upon other features than this. 

 For instance, in the Marattiaceae, 

 as will be shown later, it is probable 

 that Danaea and Christensenia 

 with their synangial sori are deri- 

 vative genera as compared with 

 Angiopteris : and as Campbell has 

 shown {E?isp. Ferns, p. 1 50, Fig. 

 126), both of these genera bear 

 small peltate scales, while Angio- 

 pteris has simple hairs. A par- 

 ticularly good instance of the 

 character of the dermal appen- 

 dages supporting comparisons 

 based on other features is seen in 

 the Schizaeaceae. In this family 

 simple hairs are prevalent. It is 

 only in Mohria, which is in so 

 many features a relatively ad- 

 vanced member of it, that broad 

 scales arepresent(Prantl,/.r.,p. 37). 



Several distinct types of dermal appendages may often be found on the 

 same plant, soft, simple, or branched hairs being scattered among the larger 

 scales in cases where the latter occur. Scales are specially developed upon 



Fig. 189. ^= scale or ramentum, of Cystopteris fra- 

 gilis: B = o{ Asplenium viridc (x about 20). (After 

 Sadebeck, from Engler and Prantl.) 



