62 



OPHIOGLOSSACEAE 



[CH. 



of xylem in the pith of O. penduliun has its interest in confirming the opinion 

 of its intra-stelar origin (Petry, Bot. Gaz. March, 1914, p. 185). 



Examination of the leaf-traces of the three genera leads to the same con- 

 clusion. In Helininthostachys and Botrychium the leaf-trace is always un- 

 divided, departing in adult plants as a sector of the solenoxylic stele. In 

 Helininthostachys the strand is composed of outer xylem with or without 

 some proportion of the internal xylem. As it departs the outer xylem is 

 completed on the adaxial side, and the protoxylem segregating into two 

 groups a Clepsydroid structure is assumed. But as it enters the petiole the 

 trace divides to form numerous strands which arrange themselves in a circle, 

 and so pass up the petiole (Fig. 353). In Botiychium the trace is derived only 

 from the outer xylem of the stele, the inner being as a rule obsolete even in 

 the axis. As it passes up the petiole it usually divides into two, which then 

 take a parallel course up the petiole. The leaf-traces of some species of 

 lioglossuni are interesting for comparison since they form an exception to 



Fig. 356. Successive transverse sections of tlie stock of Ophioi^lossitm peitdnlinii, showing 

 the origin of each leaf-trace as numerous separate strands : this is an advanced mode of 

 origin. 



the rest of the family. In the section Eu-OpJiioglossiun the leaf-trace comes off 

 as in the other genera, the single strand soon branching into three. But in 

 the sections Ophioderma and Cheiroglossa the numerous strands arranged in 

 a circle in the section of the petiole are not united into a single strand at 

 the base, but are inserted as several separate strands upon the vascular stele 

 of the stock. Comparison of Ferns at large shows that the concrete leaf-trace 

 is characteristic of primitive types, and that its separation into distinct 

 strands down to the base is a feature of those that are late and derivative. 

 Thus by this feature '^Ophioderma and '^Cheiroglossa are shown to be late 

 and derivative as compared with Eu-Ophioglossinn. The strands pass on into 

 the sterile blade, branching repeatedly as they go. The venation of the 

 juvenile leaves in Botrychium and Helminthostachys is a scorpioid sympodium 

 (Fig. 357), which is a derivative of equal dichotomy, as is shown by com- 

 parison of the young leaves of Osmunda (Fig. 416, p, 127) : but the cotyledons 

 of HelmintJiostacJiys and BotrycJiium step direct into a position that is only 

 secondary in Osvumda. The venation of the adult blade of these genera is only 



