XXXIX] 



SAFFORDIA-TRACHYPTERIS 



87 



three genera appear to form a natural series of progressive Acrostichoid 

 development, from a source related to the Cheilanthoid Ferns. There was 

 first a coenosoral fusion {Doryopteris), and then a widening of the receptacle 

 {Saffordia), till it occupies the whole lower surface {Trachypteris). The series 

 forms a close parallel to that seen in the Pteroids, in LitobrocJiia, AcrosticJmm 

 praestaiitissimuiH, and A. anremn (see p. 58). 



Fig. 641. Trachypteris pinnata (Hk. fil.) C. Chr. i. Blade of fertile frond from 

 Bolivia (Williams, 1177), intermediate between Brazil and Galapagos forms, 

 natural size. 2. Part of a fertile pinna of T. pinnata, after Hooker, showing 

 the coenosorus extending to the midrib, with the scales and sporangia in part 

 removed to show the reticulation. 



Cheilanthes Swartz 



The relation of CJieilantJies to Pellaea is a very close one. Christ defines 

 Cheilanthes, which comprises more than 100 species, as consisting of small 

 usually xerophytic plants, bearing leaves divided into minute segments, with 

 free veins. The small rounded sori are borne on the swollen tips of the veins, 

 and usually give the appearance of coalescence at maturity. The protection 

 is afforded by the more or less membranous margin, or by a projecting tooth 

 of the segment. It often appears irregular in form, and may be continuous 

 from one sorus to another, but not coherent throughout (Fig. 642). The 

 difference between Pellaea and Cheilanthes is one of detailed habit rather 

 than of essential construction of the sorus, and this is borne out by the 

 similarity of the anatomical detail. These Ferns are xerophytes of high- 

 lying plateaux, particularly of Mexico and South Africa, and they are almost 

 wholly absent from the moist equatorial zone (Christ, Farnkrdiitcr, p. 142). 



The stelar structure of the scaly stock shows a range from the simple 

 solenostele of C. Fendleri Hk., through C gracillivia Eat. with the leaf-gaps 

 overlapping, to C. lanuginosa Dav., which rarely shows a complete ring in 



