576 FILICALES 



The shoot is sometimes upright and radial, with leaves showing fths 

 phyllotaxis, as in some species of Trichomanes; or more commonly 

 creeping and dorsiventral, with the leaves arranged distichously, with 

 elongated internodes, as in many species of Trichomanes, and all of 

 Hymenophyllum. From the axis numerous scattered roots arise in most 

 species, but in some, and especially in the section Hemiphlelmim of 

 Trichomanes, no adventitious roots are formed, leafless branches of the 

 rhizome serving as substitutes. These are covered by root-hairs, which 

 resemble, however, the hairs which are normally found on axis and leaf 

 in the rooted species also. The hairs are filamentous, and ramenta are 

 absent, but peculiar scales are found in some species of Trichomanes, and 

 in some of Hymenophyllum of exposed habit the leaf is covered with 

 a hairy felt. 



The leaves in some of the larger species (H. dilatatum, australe) conform 

 in outline to ordinary branched Filicinean types, and are winged structures 

 to the base (Fig. 322). But in other cases the leaf may appeaf as a 

 widened expansion of simple form, with or without a leaf-stalk (Fig. 323), as 

 in H. cruentum, or T. reni forme, and membraiiaceiim. It would appear probable 

 that the latter are specialised and derivative forms, and they occur more 

 freely in the genus Trichomanes, which there is good reason to believe to 

 be the more specialised genus. The leaves are translucent or "filmy" 

 in texture, a feature that will be considered at length below. 



Axillary branches occur very generally in the Hymenophyllaceae, but 

 at many nodes the rudiment of the axillary bud remains undeveloped. 



The sori are marginal in all cases : the receptacle upon which the 

 sporangia are inserted in strictly basipetal sequence is traversed by the 

 direct continuation of one of the veins of the lamina ; it is surrounded 

 by the cup-like indusium, which is entire in Trichomanes, but two lipped 

 in Hymenophyllum. The sporangia vary greatly in size and productiveness, 

 but have uniformly an oblique annulus and lateral dehiscence : it will 

 be seen that these characters are closely related to the regular basipetal 

 sequence in which they are produced upon the receptacle. 



Sori and sporangia of corresponding type have been traced back to 

 early geological formations. From the upper Carboniferous, or perhaps 

 even earlier, come the doubtful sporangia of Hymenophyllites, which will be 

 considered in detail below. Meanwhile it may be noted that there is 

 reason to believe the type to have been a very ancient one. 



SPORE-PRODUCING MEMBERS. 



The comparative study of the sorus of the Hymenophyllaceae leads 

 to the conclusion that while these Ferns show the highest complexity 

 of the receptacle, the sporangia themselves are related in character 

 to more massive types, and that this will justify a systematic position 

 near to the Loxsomaceae, Dicksonieae, and Gleicheniaceae on the 



