76 



GYMNOGRAMMOID FERNS 



[CH. 



Trismeria Fee 



This genus, as maintained in Christensen's Index, contains only two species, 

 of which the better known is T. trifoliata (L.) Diels, a Fern of tropical 

 America. It has been ranked with AcrosticJuim by Linnaeus, and is included 

 under Gymnogramine in the Synopsis Filicujii, as G. {Ceropteris) trifoliata 

 Desv. The question of retention of its rank as a separate genus may be left 

 to the systematists, with the remark that while it shows an Acrostichoid 

 tendency, its close relation to Gyuinogramme is accentuated by recent 

 observations (647). 



The Fern is well figured in Hooker's Garden Ferns, Plate IV. It has an 

 erect stock bearing leaves arranged alternately, the axis and leaf-bases being 

 covered with brown scales. The leaves 

 bear numerous subcoriaceous pinnae, the 

 lower of which are usually ternate, the 

 upper undivided. The distal pinnae are 

 fertile, the whole lower surface appearing 

 to be covered by sporangia and glandular 

 hairs, with a characteristic white or yellow 

 secretion of wax (De Bary, Camp. Anat. 

 p. 99). The venation is always open. 



The axis is traversed by a solenostele, 

 which opens to give off successive leaf- 

 traces. These consist each of two vascular 

 straps, which are already separated from 

 one another before they are detached from 

 the stele (Fig. 632). The pinna-traces of 

 the basal pinnae are of extra-marginal 

 origin from the still divided straps of the 

 rachis, but these unite towards the distal 

 region, and the pinna-traces are there 

 marginal in origin. This change within a 

 single leaf shows that there is no essential 

 difference between the two types of origin 

 of the leaf-trace: it appears to depend 

 chiefly upon the size and the degree of 

 curvatureof the vascular tract of the rachis. 

 A comparison of the vascular system of 

 Trismeria with that of Gymnogramine 

 japonica (see Vol. i, Fig. 160) shows that 

 though both have the divided leaf-trace, the former is nearer to a primitive 

 solenostele than the latter, differing from it in the absence of those per- 



Fig. 632. Reconstruction of the stele ot 

 Trismeria showing solenostele, with short 

 leaf-gaps and binary leaf-traces. (After 

 J. McL. Thompson.) 



