XXXIX] CERATOPTERIS 71 



strands that cross the leaf-gaps. At first there are no medullary strands, 

 though these arise later. The earlier leaves show a leaf-trace of two pairs of 

 strands : the lower pair springs from a median point at the base of the leaf- 

 gap, and they either fuse at once laterally, or are connected later by a 

 cross-strand. They supply the abaxial curve of the rachis. The second pair of 

 strands arise high up on the leaf-gap, and they are connected by one or two 

 cross-strands. They supply the adaxial curve of the rachis. Higher up still 

 two additional leaf-strands may arise, one at each side of the base of the 

 leaf-gap. At first the leaves receive no strands from the medullary system, 

 for it does not exist. But as the axis increases medullary strands arise, and 

 the later leaves receive strands direct from them, which branch and anastomose 

 in the rachis, but finally disappear by fusion with the bundles of the leaf- 

 trace itself The supply to the pinnae springs from the margins of the outer 

 series of the rachis, the connections being with both the abaxial and the 

 adaxial curves of the highly disintegrated system (compare Vol. I, p. 173, 

 Figs. 169, 170). 



It thus appears that the vascular system of Ceratopteris is cognate with 

 what is seen elsewhere in large Ferns of various affinity. The axis is dictyo- 

 stelic with a medullary system. The petiole shows high disintegration of 

 the primary trace, which is reinforced in the older leaves by medullary 

 connections: and the origin of the pinna-traces is extra-marginal. All these 

 conditions are probable for a sappy water plant, though they suggest an 

 advanced state of adaptation. This is also indicated by the reticulate vena- 

 tion. 



A greater interest attaches to the soral conditions, which present strangely 

 conflicting features. The fertile leaf-segment is lanceolate in outline: the 

 sporangia that it bears are not associated into sori, but are seated solitary 

 upon the anastomosing veins, so that they appear in irregular rows parallel 

 to the margins of the segment : these overarching protect the young sporangia 

 in the absence of any more definite indusium (see Kny, 631). The sporangia 

 themselves are large and short-stalked, the stalk consisting of a rosette of 

 five or six cells. Each sporangium arises from the leaf-surface by the out- 

 growth of a single cell, in which the first segment-wall impinges directly on 

 the basal wall, or sometimes on one of the oblique lateral walls (Fig. 630), 

 after the manner of Ferns with sporangia larger than those of the typical 

 Leptosporangiates (see Fig. 238, Vol. I, p. 244). The sporangial head is 

 spherical, and very variable in structure and contents (Fig. 631). The annulus 

 is usually vertical and interrupted at the insertion of the stalk. It may consist 

 of very numerous cells: as many as seventy have been counted by Benedict 

 (642), but forty is usual, though the numbers may be much smaller, and it 

 is stated that sometimes the induration may be absent altogether (Hooker, 

 I.e. p. 236). While the annulus may thus be sometimes incomplete, at others 



