568 



FILICALES 



were indusiate, as in Matonia itself. The difference does not seem to 

 be an essential one, and in face of the correspondence of the Ferns in 



question in other respects it 

 c cannot be held to invalidate 



the reference of these, and of 

 certain other Mesozoic Ferns 

 to the family of the Maton- 



meae. 



ANATOMY. 



FIG. 318. 



A= pinnule of Laccopteris Woodward i from the inferior 

 oolite of Yorkshire : the hemispherical bosses show the 

 position of the sori (No. 217, Brit. Mus.). B = pinnule of 

 Laccopteris polypodioides with sori and soral impressions. 

 Upper shale, Gristhorpe Bay (No. 2522, Brit. Mus.). C= 

 pinnule fragment from the inferior oolite of Stamford (No. 

 52867, Brit. Mus.). (After Seward, from drawings by Miss 

 G. M. Woodward.) 



The mature rhizome of 

 Matonia shows the most com- 

 plicated solenostelic structure 

 known in Ferns : in the young 

 stem, however, simpler condi- 

 tions are found which suggest 

 how the final condition was probably arrived at. In the most complex 

 rhizomes three concentric vascular rings may be found embedded in 

 parenchyma, and each showing the typical solenostelic structure. Each is 

 limited externally and internally by an endodermis and pericycle, while 

 between these in each is a continuous ring of xylem, with phloem on either 

 side of it. The arrangement of this solenostelic structure is represented 

 diagrammatically in Fig. 319, together with its connections with the leaf- 

 trace. The latter is in these Ferns one continuous band, with involuted 

 margins, which are shown in Fig. 319 c: this drawing also indicates that 

 foliar gaps occur, and shows how the leaf-trace is directly continuous with 

 the outer and middle of the concentric rings at the node. There may also 

 be a connection with the inner ring ; but this occurs at some little distance 

 from the actual node, and so is not shown in the drawing. The result 

 is that the whole system is connected, but only at intervals of its whole 

 length, while there is also connection through the leaf-gaps between the 

 parenchymatous tracts in which the cylinders are embedded. 



The ontogeny gives the suggestion how this complicated structure is 

 to be placed in relation to that of other Ferns. The young axis contains 

 at first a slender protostele ; but this simple stele soon expands, and a 

 strand of phloem appears in the midst of the xylem. This internal phloem 

 appears to be a phloem-pocket decurrent from the adaxial surface of the 

 second leaf, but there is as yet no true leaf-gap. The stele soon widens 

 into a solenostele with internal endodermis and central parenchyma. 

 Meanwhile at the nodes a ridge of xylem projects internally, which becomes 

 more prominent at subsequent nodes, and is continued forwards into the 

 internode further and further at successive nodes, till that of one node 

 eventually connects with a similar xylem-dilatation of the next node 

 (Fig. 3 19 A). A continuous central strand is thus produced, which is 

 connected at the nodes with the outer cylinder. 



