214 ORIGIN AND RELATIONSHIPS OF THE EUSPORANGIATAE 



sacea?. In the Marattiacea? small cauline bundles (commissural bundles) may be 

 developed at later stages, but these arc insignificant compared with the complex of 

 united leaf traces. 



The antithetic theory of alternation implies that the sporophvlls arc older 

 structures than the sterile leaves, and those ferns in which the sporogenous function 

 of the sporophylls is most pronounced ma)' be assumed, other things being equal, 

 to be the most primitive. In this respect, as well as in the usually monophyllous 

 condition, the Ophioglossacea? are distinctly more primitive than the Marattiaceae. 

 The sporangiophore or fertile leaf segment is a practically independent structure, 

 being differentiated at an extremely early period in the development of the leaf. 

 In the Marattiacea? the sporangia are subordinate and the leaves upon which they 

 are borne usually differ in no respect from the sterile leaves. The most marked 

 exception to this is Datura, in which the sporophylls differ decidedly from the sterile 

 leaves and the synangia are much larger than those of the other genera, although 

 the leaves themselves are usuallv smaller. 



Bower thinks that the circular synangium of Kaulfussia is the most primitive 

 tvpe among the existing Marattiacea?, but there is some reason to doubt the sound- 

 ness of this conclusion; at any rate, on theoretical grounds, the large synangia and 

 contracted sporophylls of Dana- a must be assumed to be more primitive than the 

 type of leaf found in Kaulfussia. In regard to the character of the sporophylls, 

 tnerefore, none of the living Marattiacea? can be regarded as being very primitive. 

 All of the oldest fern fossils show the sporangia to be borne upon special leaves or 

 leaf segments, in which the lamina is nearly or quite absent (Scott 1, Bower 9). 

 In this respect, therefore, these ancient fossil ferns were more like the ( )phiogloss- 

 aceae than like the Marattiace;e, although their sporangia came nearer to the type 

 of Marattiacea?. It is by no means impossible that these oldest ferns, e.g., the 

 Botryopterideae, were related to the Ophioglossaceae. 



The single apical cell found in the stem apex throughout the life of the sporo- 

 phyte in Ophioglossum is probably a more primitive condition than the group of 

 cells found in Angiopteris. It still remains to be seen whether the single apical cell 

 found in the other Marattiace;e in their early stages is persistent throughout life or 

 is replaced, as in the roots, by a group of initial cells. 



The single axial strand of collateral structure throughout cotyledon and root 

 may be taken as the starting point for two types of vascular skeleton which have 

 arisen from it. The first is that of Ophioglossum, where, with the development of 

 the new kaves, there is built up the wide-meshed cylindrical network or dictyostele, 

 cjmposed of single collateral leaf traces. A further development of the same type 

 results in the much more complicated dictyosteles of the Marattiacea?, where, more- 

 over, the collateral bundles are replaced by concentric ones. This greater com- 

 plexity is due primarily to the much larger leaves of the Marattiacea?, in which the 

 leaf traces are compound. In the earlier stages of these forms, however, we have 

 seen that the young leaf traces are single anil tin structure of the vascular skeleton 

 exactly as it is in Ophioglossum. Of the Marattiacea', Kaulfussia more nearly 

 retains this primitive condition than the other genera and next to this comes Datura. 

 while further removed from the primitive type is the exceedingly complex skeleton 

 found in the massive stem of Angiopteris. The concentric bundles, characteristic 

 of flu- Marattiaceae, are presumably of secondary origin and we find that in the 

 early bundles, especially of Datura, a true collateral structure is present. 



The second type of skeleton is that found in Botrychium and Helminthostachys, 

 This is a solid, hollow cylinder with inconspicuous leaf <?,aps, resulting from the 

 union of the broad leaf traces, which fuse completely to form this hollow stele. I hat 



