82 THE OPHIOGLOSSALES 



COMPARISON OF THE YOUNG SPOROPHYTES OF THE OPHIOGLOSSACE^. 



If, as we believe, the type of sporophyte found in Ophioglossum moluccanum 

 is really primitive, we may assume that the sporophyte at first had a single axial 

 stele, collateral in structure and essentially the same in leaf and root. This primitive 

 sporophyte had no stem at all, but consisted simply of leaf and root. From the 

 primitive vascular skeleton, composed of a single unbranched strand, we can derive 

 the different types characteristic of the older sporophyte in the three genera. As 

 to the first origin of the stem apex, we can only conjecture; whether it originally 

 arose, as it does in Ophioglossum, as an endogenous structure repeating, as it were, 

 the origin of the primary root, we have no means of knowing, but this seems to be 

 the most probable explanation of the origin of the stem apex in the primitive sporo- 

 phyte from which are descended the different types of the Ophioglossaceae. After 

 the establishment of the stem apex the secondary leaves contributed their quota to 

 the developing skeleton of the sporophyte. In Ophioglossum these leaf traces remain 

 largely free and anastomose only to a limited extent, thus giving rise to the open 

 tubular dictyostele with very large meshes. The structure of the individual strands 

 of the dictyostele is essentially the same as that of the free leaf traces. 



In Helminthostachys the early leaf traces fuse completely and there is formed 

 a solid stele in the younger internodes with a central xylem core, composed of the 

 united xylems of the two leaf traces. These leaf traces are approximately collateral 

 in structure, although it may be that they have a small amount of phloem upon 

 their inner face. After entering the petiole of the young leaf, however, these assume 

 a distinctly concentric form. As the leaves increase in size their traces become 

 broader and in section appear more or less crescentic, so that when the leaf traces 

 come together there is left between them a certain amount of the ground tissue which 

 after they have united appears as a pith lying inside of the tubular stele. This 

 pith, however, it must be remembered, is not part of the stele proper, but is merely 

 an included portion of the ground tissue. With the complete fusion of these two 

 broad leaf traces the tubular form is established and the wood appears in section 

 as a continuous ring. In Botrychium, especially in the large forms like B. virgin- 

 tanum, the tubular condition which is secondary in Helminthostachys is established 

 at once; this is probably to be explained by the fact that the vascular bundles of 

 the first leaves are much better developed, there being two strands in the cotyledon 

 and in the second leaf, and the leaf traces belonging to these are correspondingly 

 broad and on fusing include at once a certain amount of the ground tissue, so that 

 the stele appears tubular from the beginning. Botrychium virginianum undoubtedly 

 represents the most specialized type of the Ophioglossaceae, and the development 

 of the cambium with a permanent secondary thickening of the wood is an evidence 

 of a higher degree of specialization in the vascular system than is found in any other 

 living Pteridophyte. While a very slight indication of this secondary thickening 

 has been found in Ophioglossum, and I have also noted some slight traces of it in 

 Helminthostachys, there is never developed in these the genuine cambium ring, such 

 as we find in Botrychium virginianum. In the development of the spiral protoxylem 

 elements Helminthostachys differs from the other Ophioglossaceae and suggests the 

 true ferns. In the early development of its vascular system there rare strong sugges- 

 tions of some of the Marattiaceae, especially Kaulfussia and Danaa. The develop- 

 ment of concentric bundles in the petiole in Helminthostachys and Botrychium 

 also suggests the Marattiaceae. 



Assuming that the collateral bundle, which is typical of the stem in all of the 

 Ophioglossaceae and occurs also throughout in Ophioglossum, is primary, the con- 



