136 EMBRYOGENESIS IN PLANTS 



epibasal segment may form a large and massive root, or a primary root 

 may be formed from one side and a second root from the opposite side. 

 These developments are evidently related to the nutrients taken up 

 from the prothallus by the massive foot. The embryo grows to a large 

 size before it emerges from the prothallus, and the primary root may 

 attain to a length exceeding 2 cm before there is any evidence of the 

 organisation of the shoot apex and the formation of the first leaf. The 

 apical bud is probably formed endogenously in the primary root as in 

 O. moluccaimm. As the prothallus of O. pendulum is long-lived, it is 

 considered that the young sporopliyte may continue its underground 

 saprophytic existence for an indefinite period. 



From the fact that the shoot apex originates near the base of the 

 primary root, i.e. near the centre of the embryo, it could be argued that 

 it is not necessarily organised from a later-formed growth centre but 

 that it is the original distal pole of the embryo which has been delayed 

 and become displaced by the extensive development of the primary 

 root. In short, the embryonic development in O. pendulum is in 

 essentials like that of O. vulgatum, the differences being of degree rather 

 than of kind. The same underlying biochemical pattern is present in 

 both, and is never obliterated, however much the initial organogenic 

 development may be modified by nutritional factors. Because the shoot 

 apex exists for some time in a histologically rudimentary condition it is 

 not necessarily completely non-functional. In the several species of 

 Ophioglossum, the first leaf is always a dorsiventral structure, with a 

 collateral vascular strand in which the xylem is on the adaxial, i.e. the 

 apical, side. 



BOTRYCHIUM LUNARIA AND OTHER SPECIES 



In external morphology and internal structure Botrychium closely 

 resembles Ophioglossum and from this it may be inferred that it has a 

 similar underlying developmental pattern. In the smaller species of 

 Botrychium, e.g. B. simplex and B. lunaria, which closely resemble 

 O. vulgatum in size and organisation, the embryogeny is exoscopic, the 

 first, basal wall is transverse, and the subsequent divisions yield a typical 

 octant stage, Figs. 30, 3 If. No suspensor is present. At the octant stage 

 the embryo is subspherical or ellipsoidal. On further development and 

 cell division the exact boundaries between the epibasal and hypobasal 

 regions are not clearly defined and the subsequent organogenic develop- 

 ments cannot readily be related to the initial segmentation. However, 

 in B. simplex, it seems probable that the foot and root are of hypobasal 

 origin and the leaf and shoot apex of epibasal origin (Campbell, 1940). 

 If so, the embryogeny in this species would be generally comparable 

 with that of many other ferns. The young embryo, nourished by a 



