286 PROTOCYATHEACEAE [ch. 



petioles. In large leaves it may divide into three portions, but these unite 

 again upwards, showing as in many large petioles a corrugation corresponding 

 to the constituent "divergents": but it does not disintegrate again, showing 

 in this its primitive state. The pinna-traces are extra-marginal in origin, as 

 in the Cyatheaceae and the Gleicheniaceae (Vol. i. Fig. 170, p. 174). The 

 leaf-structure is as in the Cyatheaceae, excepting that vein -fusions never 

 occur in LopJiosoria. The vascular supply to the stolons arises external h' 

 from the leaf-bases, and as they are usually solenostelic from the first, each 

 appears as a diverticulum from the axial stele, just below the leaf In all 

 these features Lophosoria is like a primitive Cyatheoid, which had not 

 departed far from typical solenostel}'. But comparison with the solenostelic 

 G. pectinata shows similarity in all essential points, allowance being made in 

 the latter for the structural effect of the contracted leaf-base. These two 

 Ferns form in fact a structural bridge between the protostelic Gleicheniaceae 

 and the dictyostelic Cyatheaceae. 



Fig- 550. Transverse section of stem of Lophosoria, 

 from which a leaf-trace has just departed, and prepara- 

 tion is being made by thinning of the solenostele for a 

 second, and even a third. (Natural size.) The scleren- 

 chyma is dotted, and vascular tissue black. The leaf- 

 trace is divided into three parts. 



Sporangia 

 The sporangia not only of a sorus but of a pinnule of LopJiosoria are 

 formed simultaneously, a state characteristic of the Gleicheniaceae and other 

 primitive Ferns rather than of the Cyatheaceae. Each sporangium is almost 

 spherical, and is seated on a short thick stalk, which shows six or more cells 

 in transverse section: this also is comparable with Gleicheniaceae. The 

 annulus is oblique, and appears as a complete ring defining the almost equal 

 distal and basal faces. It is usually a single row of cells, but it may 

 occasionally be doubled near to the stomium, as happens occasionally also 

 in Gleichenia (Fig. 551). The stomium is lateral, and not highly differentiated, 

 its cells being variable in number and in position. The development of both 



