240 HYMENOPHYLLACEAE [ciL 



receives only a single strand, which widens out upwards into a collateral 

 structure, with the form of a more or less clearly curved horse-shoe. 



Comparison of the anatomical structure of living species shows a close 

 similarity among the larger species, such as T. renifornie and H. scabrimi 

 or dilatatinn (Fig. 510). This structure finds its parallel in Anachoropteris, 

 one of the Botryopterideae (see Vol. I, Fig. 117). If the small central 

 tracheides oi AnacJioroptcris are protoxylem, as seems highly probable, the 

 agreement is very close, the differences being such as would be due to the 

 two-fifths divergence and accommodation to the size-factor, as against 

 a smaller size and distichous phyllotaxy. The protostelic origin of the leaf- 



Fig. 510. Transverse section of a node of Hyinenophylliim dilatatum v. 

 Fcrstcrianiiin. Stele of rhizome to the right, leaf-trace to the left. 

 //i = phloem: /.v = protoxylem : /= lower xylem-bands : ?< = upper xylem 

 band. ( x 200.) (After Boodle. ) 



trace, and the relation of the axillary bud are also points of similarity. This 

 resemblance to a very ancient Fern suggests the recognition of the living 

 species named as probably primitive in the living family, while from that 

 central point other species of Hymenophyllnm and Trichomanes would 

 have diverged along their several lines either of reduction or of other 

 specialisation. 



SoRi AND Sporangia 

 The receptacle of the sorus in the Hymenophyllaceae is always marginal 

 in origin. It may be more or less elongated, and is traversed by the continu- 

 ation of a vein of the lamina. In Trichomanes it persists after the sporangia 

 are shed as a stiff bristle, hence the generic name. It is surrounded at the 

 base by a cup-shaped, or two-lipped indusium. Upon this receptacle the 



