250 HYMENOPHYLLACEAE [CH. 



they show similarity to several protostelic families of the Simplices, but 

 more particularly to the Schizaeaceae. The Hymenophyllaceae are to be 

 looked upon as probably of early origin, but ending as a blind line of 

 descent, characterised by specialisation of both generations to a hygro- 

 philous habit, which takes the form of simplification. The more robust 

 species with large spore-output per sporangium, such as Trichomanes reni- 

 forme and Hyjiienophylhim dilatatiun, appear to occupy a central position 

 phyletically: Trichovianes shows the greater specialisation, and is on that 

 account to be regarded as the farthest removed from the original source. 

 The Hymenophyllaceae comprise two substantive genera: 



I. Trichomanes Linne, 1753. Species 228. 



The prothallus is usually filamentous: the indusium tubular or flask- 

 shaped. 



II. Hymenophyllinn Smith, 1793. Species 231. 



The prothallus is a flat expanse or ribbon: the indusium two-lipped. 



These genera have been variously sub-divided, and the numerous species grouped : but 

 with few exceptions the sub-genera or groups appear to be of use rather for the recognition 

 and designation of species than indicative of phyletic relations. Therefore they need not 

 be detailed here, but reference may be made to systematic works. Certain groups or species 

 that bear characters of phyletic significance may however be noted. For instance in 

 Trichomanes the section Cardiomanes, containing the isolated, but probably central 

 species T. rettiforme, with its primitively equal dichotomy of the veins, but fully webbed 

 lamina, and many layered structure: its robust texture and vascular system, and high 

 spore-output. Also the section Feea Bory, comprising four heterophyllous species, all of 

 the New World, of which the most remarkable are T. spicahnn Hedw. (Fig. 504, D), 

 and T. elegans Rudge, the latter with erect, tufted shoot, sterile leaves pinnate and webbed, 

 with vein-fusions, and narrow fertile leaves with open venation. This is morphologically 

 the most advanced type of all. On the other hand thalloid leaves are found in T. mem- 

 branaceuvi L. and Lyallii Hk. (Fig. 504, B\ while many are minute epiphytes, culminating 

 in T. Goebelianiun (Fig. 506). Many of the species are characterised by very low spore- 

 output. 



Hyjnefwphyllicin shows less variability, and a prevalent creeping habit, with "Spheno- 

 phylloid" leaves. H. criientinn Cav. is exceptional in having a fully webbed lamina (Fig. 

 505,.^). The spore-output is usually higher than in Trichomanes^ i.e. more primitive: 

 thatof //■. r/^«<^;7^^wzjt' is unusually high (356-512), showing that prolific production does 

 not necessarily follow the size of the plant. 



BIBLIOGRAPHY FOR CHAPTER XXVII 



503. Engler & Prantl. Naturl. Pflanzenfam. i, 4, p. 91, where the earlier literature is 

 very fully cited. 



504. Campbell. Mosses and Ferns. 3rd Edn. p. 372 etc. 191 8, where there is a full 

 citation of literature. 



505. Prantl. Die Hymenophyllaceen. Leipzig. 1875. 



506. Christ. Die Farnkraiiter der Erde. Jena. 1897. 



