50 



THE OPHIOGLOSSALES 



through horizontally. At the slightly projecting apex there is a single apical cell, 

 although it is not always quite certain which is the apical cell and which is its 

 youngest segment. The broad base of the cotyledon is extended laterally, like the 

 stipules of the older leaves, and there is thus inclosed a slightly depressed area, very 

 much as in the embryo of Ophioglossum vulgatum, and within this is situated the 

 stem apex, close to the base of the cotyledon, which bends over it so as to leave 

 only a narrow space above the stem apex. A section across the base of the cotyledon 

 shows a group of small cells indicating the section of the young vascular bundle 

 which lower down (fig. 34, C) joins the young bundle of the primary root. 



The relative position of the young organs just before the root ruptures the 

 calyptra is best seen in a longitudinal section. Such a section (fig. 35, A^ shows the 

 very large foot, occupying approximately half of the embryo, and deeply embedded 

 in the prothallium. Above this is the root, occupying the major part of the epibasal 

 region of the embryo and varying somewhat in position, perhaps due to the early 

 divisions in the young embryo. It may lie in a plane almost coincident with the 

 cotyledon, or it may make a marked angle with the latter. In the former case the 



Fig. 35. 



A. Median section of a young sporophyte of Botrychiuw virginianum about to emerge. X about 50. 



B. An older stage; /^, second leaf; r^, second root. X20. 



young vascular cyhnder is continued almost straight into-the cotyledon; in the 

 latter it bends sharply upward to meet it. 



The stem apex, which is usually more or less oblique, is small and incon- 

 spicuous, but usually a single initial cell may be made out without difficulty, although 

 sometimes it is not easy to distinguish this from the younger segments which have 

 been cut off from it, as the apical meristem is very shallow, and in longitudinal 

 section has the appearance of a columnar epitheHum.!^i|There seems to be, at least 

 in the earlier stages of development, some variation in the form of the initial cell, 

 which may have a pointed base, or may be truncate below, and while later it 

 usually shows the form of a three-sided pyramid, in these earlier stages it often 

 approximates the truncate form found in Ophioglossum moluccanum. 



The apical meristem of the stem is very limited in extent and, so far as could 

 be made out, the segmentation at first does not follow any regular scheme. While 

 in both root and cotyledon a central strand of procambium is developed at a very 

 early period, no trace of anything which can he interpreted as a "stele" is formed in 

 the young stem. The tissues derived from the further segmentation of the apical 

 meristem remain undifferentiated parenchyma and contribute only to the central 

 pith of the hollow woody cylinder which later traverses the axis of the young 



