THE EMBRYO 43 



course, it is quite possible that the peculiar origin of the definitive sporophyte in 

 O. molaccanum and O. pedunculosum is secondary, but this is by no means neces- 

 sarily the case. However, it seems highly probable that the extraordinary develop- 

 ment of the roots in 0. vulgatum and O. pendulum and the protra<:ted subterranean 

 life in these species constitute a secondary phenomenon associated with the pro- 

 nounced saprophytic life of the gametophyte. 



The apex of the shoot lies in a narrow depression between the base of the leaf 

 and a narrow ridge which extends around it on the side opposite the leaf base. This 

 ridge is the beginning of the conical sheath characteristic of the shoot apex of the 

 older sporophyte. A transverse section of the young apex at about this time shows 

 that the apical cell is triangular in outline. 



The first root of the young bud does not emerge until the leaf is nearly complete. 

 From this time on the further growth is due to the activity of the stem apex, from 

 which new leaves and roots presumably are developed in the same way as in other 

 species that have been studied. How long it is before fertile leaves are formed was 

 not ascertained, but in the rapidly growing species of a tropical climate it is likely 

 that this takes place before long. The occurrence of very small fertile individuals 

 (fig. 55, B) points to this. 



THE EMBRYO OF OPHIOGLOSSUM VULGATUM. 



The embryo of 0. vulgatum (Bruchmann 1) differs from that of both 0. 

 pendulum and 0. moluccanum in its development, but in the earlier stages it closely 

 resembles the former species. As in O. pendulum, the root is the first organ to be 

 developed and it reaches a large size before there is any indication of the formation 

 of a stem apex or cotyledon. Bruchmann states that the root apex arises from the 

 hypobasal half of the embryo, but his figure (fig. 19, A) of the young embryo, where 

 the root apex is just visible, closely resembles a corresponding stage in 0. pendulum, 

 where the root is certainly of epibasal origin; and, to judge from the elongated form 

 of the two-celled embryo which Bruchmann figures, one is inclined to believe that 

 the basal wall is really at right angles to the long axis of the embryo, and not parallel 

 with it, as he figures, so that the whole of the hypobasal part might be interpreted 

 as the foot, while the root would be of epibasal origin, as it is in O. pendulum. 



The next stage figured by Bruchmann (fig. 19, 5) is very much like the type of 

 O. pendulum, where only one root was developed at first, and in this case also we are 

 inclined to consider the whole of the enlarged base of the embryo as the foot. 



Before the cotyledon and stem apex can be recognized the first tracheary tissue 

 of the root has already been developed, and about the same time the apex of the 

 second root can be seen arising near the base of the primary root (fig. 19, C). 



The cotleydon arises near the base of the root, upon the upper side of the 

 embryo, and forms a small conical protuberance, which grows from a definite apical 

 cell. At the base of the cotyledon, on the side turned away from the root apex, a 

 shallow depression is formed, and in this there may be seen a single large superficial 

 cell, which is apparently the apical cell of the very limited stem apex. Inclosing the 

 cotyledon and the stem apex is an elevated ridge which grows up about them and 

 finally forms a sheath, which rapidly grows so as to include the bud within a cavity 

 completely closed except for a narrow canal which opens outward. 



While the cotyledon and stem apex are thus formed from superficial tissue in 

 0. vulgatum, their early inclosure in the sheath suggests that we have to do with a 

 condition intermediate between the completely endogenous shoot apex in 0. moluc- 

 canum and the entirely exogenous shoot in Botrychium. 



