52 



THE OPHIOGLOSSALES 



is in Ophtoglossum and Botrychium lunaria, approaches the circinate form of that of 

 the Marattiaceae and the typical ferns. The young vascular bundle is now clearly 

 evident, lying somewhat toward the inner side of the leaf, and it can be readily 

 followed downward until it joins the root bundle, with which it is continuous. 



In B. virginianum, while the cotyledon is still quite small, the second leaf 

 appears close to the stem apex and nearly opposite the cotyledon, the sheathing 

 base of which surrounds the stem apex, together with the young second leaf. The 

 growth of the second leaf is also probably from a tetrahedral apical cell, and this 

 is the case with all of the later leaves. While the second leaf is still very small, 

 there begins the differentiation of the corresponding leaf trace, which joins the 

 bundle of the primary root close to the point at which it gives off another bundle 

 destined for the second root, the apical cell of which is cut out from the tissue near 

 the base of the second leaf, at a point almost directly opposite the cotyledon. 

 Indeed, the second root may be said to bear much the same relation to the second 

 leaf that the primary root does to the cotyledon (fig. 35, jB). 



Fig. 36. — Botrychium lunaria (after Bruchmann). 

 A, B. Young embryos. X225. 

 C, D. Older embryos. The cotyledon and stem apei, st, are developed much later than in B. virginianum. 



The cotyledon in B. virginianum (Hg. 7) is extraordinarily developed, reaching 

 a size that probably is unequaled by any other fern. Its slender petiole reaches 

 a length of 5 to 6 centimeters, and the lamina, unlike the simple oval primary leaf of 

 Ophioglossum, is ternately divided and the segments deeply cut. The venation, 

 instead of being reticulate as in Ophioglossum, is apparently pinnate, but this is 

 really the result of an unequal dichotomy, as it is in the ultimate branches of the 

 veins in most ferns. 



The base of the petiole forms a stipular sheath like that found in the later 

 leaves, and it is traversed by two vascular bundles, which unite into a single trace 

 before joining the bundle of the root. 



While in B. lunaria all of the early leaves remain rudimentary, and the first 

 one to appear above ground is a fertile one, there are sometimes intermediate stages 

 which may show a small ternate lamina and traces of the fertile spike, although they 

 never appear above ground (see Bruchmann 2, fig. 50). 



If horizontal sections of the young sporophyte are examined, at about the time 

 the cotyledon first emerges (fig. 41), the latter will be seen to have the form of a 



