254 THE BOOK OF CHOICE FERNS. 



peculiar forms and of a leathery texture, as may be readily judged from 

 P. (Doryopteris) palmata and P. sagittifolia. 



Whatever their dimensions, the above-named plants have their fronds 

 produced from either single or tufted crowns ; but there are other species in 

 which the fronds are produced from and disposed along a creeping rhizome. 

 Foremost among the strongest growers of these are P. aquilina (our common 

 Bracken) and P. incisa, while among the smaller-growing species P. scaherula 

 may be named as one of the most distinct. If we compare the gigantic 

 drooping P. moluccana and the equally strong-growing but upright P. tremula 

 with such species as P. pedata and P. sagittifolia^ the fronds of which seldom 

 attain more than 9in. in length, we at once realise a striking contrast, in 

 shape as well as in dimensions. 



Pteris, in Hooker and Baker's " Synopsis Filicum," is Genus 31, and 

 forms an important portion of tribe Pteridece. Its distinguishing characters 

 reside in the disposition of the sori (spore masses), which are marginal (attached 

 to the edge of the leaflets or of the leafits), and disposed in a narrow, 

 continuous line, occupying a slender, filiform (thread-like) receptacle in the 

 axis of the involucre, which is of the same shape as the spore masses and 

 usually of a parchment-like texture. This involucre, which at first quite covers 

 the spore masses, eventually becomes more or less spreading as ripening 

 proceeds. In some species the veins are free, while in others they are more 

 or less anastomosing (intercrossing each other), and it is principally on 

 these latter characters that the genus has been subdivided into the following 

 sections : 



Amphiblestra (Am-phib-le'-stra), Presl. This sub-genus, which, up to 

 the present, comprises but one species, has veins copiously intercrossing each 

 other and free veinlets. 



Campteria (Camp-te'-ri-a), Presl. A sub-genus composed of a few strong- 

 growing species with veins all free, except that those of the last divisions 

 but one are more or less connected by arching veins at the very base. 



Doryopteris (Dor-y-op'-ter-is), /. Smith. In this sub-genus, of thoroughly 

 distinct outward appearance, the fronds are small, sagittate (arrow-shaped), or 

 sub-pedate (their subordinate parts having a palmate arrangement), and borne 

 on distinct footstalks. The veins copiously intercross each other, and they 

 have no free veinlets. 



