THE EMBRYO 



35 



fairly complete series of embryos was obtained and the development followed quite 

 satisfactorily. 



In O. moluccanum I found two quite young embryos, the youngest consisting 

 of two cells (fig. 1 8, B), the other much more advanced, with the cotyledon already 

 differentiated and the beginning of the primary root recognizable. In the first 

 embryo the basal wall was nearly transverse to the axis of the archegonium and, to 

 judge from the arrangement of the organs of the older embryo, it looks as if the whole 

 of the hypobasal region formed the foot, the epibasal half giving rise to the cotyledon 

 and root. The older embryo (fig. i8, C) was cut longitudinally in the plane of the 

 cotyledon, which at this time comprises pretty much the whole of the upper part of 

 the embryo, the hypobasal region being occupied mainly by large cells which con- 

 stitute the foot. Unfortunately, in this series the section containing the apex of the 

 leaf was missing, and so it is impossible to say whether at this stage a definite apical 

 cell is present in the cotyledon; but, as in somewhat older stages such a cell seemed 

 to be always present, it is probable that there was an apical cell in the cotyledon of 

 the embryo in question. At the base of the leaf, and almost in the center of the 

 embryo, there was a group of actively growing cells, evidently marking the position 

 of the root apex, which arises deep in the tissue of the embryo, very much as we 

 shall see to be the case in the Marattiaceae; and it seems probable that in 0. moluc- 

 canum, as in Dancea, the root grows downward through the foot and in a direction 

 coincident with the axis of the young cotyledon. 



Fig. 19. — Ophioglossum vulgatum (after Bruchmann). 



A. Median section of a young embryo. Xi6o. B. An older embryo. X25. 

 C, D. Older embryos, showing beginning of apical bud, b; r, root. X25. 



The cotyledon grows upward and soon ruptures the overlying prothallial tissue, 

 while the root grows down in the opposite direction and pierces the prothallium at a 

 point some distance below where the leaf emerges. As the root grows downward 

 through the foot the latter becomes unrecognizable, its outer cells remaining, 

 however, as a zone of large cells encircling the equatorial region of the very much 

 elongated bipolar embryo. 



The young root very early develops a tetrahedral apical cell, like that of the 

 later roots. This cell is probably cut out from the central tissue of the embryo, close 

 to the base of the leaf. The cell r in fig. i8, C, to judge from its position and the 

 arrangement of the cells around it, is probably the initial cell of the primary root. 



The young cotyledon grows rapidly and has first a conical form (fig. 23, B), 

 terminating in a definite apical cell. As it grows it develops a small oval lamina 

 and a slender petiole, and presently the little green leaf appears above the surface 

 of the earth. 



The embryo of 0. vulgatum differs remarkably from that of 0. moluccanum in 

 the late development of the leaf. Bruchmann was unable to obtain the younger 

 stages of the embryo, so that the origin of the different members is still somewhat 

 obscure. In this species it is the root which develops first, and it soon becomes 



