EMBRYOGENESIS IN EUSPOR ANGI ATE FERNS 135 



to this structure. The second root does not emerge until the second leaf 

 is nearly complete: its stele joins the leaf stele near its conjunction with 

 the first root. Thereafter, in CampbelTs account, the development of 

 the sporophyte is attributed to the activity of the shoot apex. 



Considerable difficulties have to be overcome in any attempt to 

 explain these developments in O. moluccamuu. CampbclTs data arc 

 admitted by him to be somewhat incomplete. As the hypobasal seg- 

 ment soon becomes enlarged and parenchymatous, it is perhaps not 

 surprising that the primary root has its inception in some of the more 

 deeply seated tissue which has remained meristematic. Again, although 

 the whole of the epibasal segment seemingly gives rise to the cotyledon 

 or first leaf, this leaf is not an organ of completely radial symmetry. It 

 first appears as a conical structure but its inherent dorsiventrality 

 becomes apparent on further growth. From this the present writer 

 would conclude, on the basis of a biochemical theory of embryogenesis, 

 that, as in O. rulgatum, the epibasal segment has two growth centres: 

 one of these early becomes active as the first leaf, whereas the other 

 remains relatively inactive as far as the development of structural 

 organisation is concerned. But, later, this inconspicuous but persistent 

 growth centre develops and becomes organised as the shoot apex. 

 Because the vascular strand of the second leaf becomes conjoined with 

 the root stele, it does not necessarily follow that this leaf is independent 

 of the shoot apex. Since the third and all subsequent leaves are formed 

 at the shoot apical meristem, it would be somewhat exceptional if the 

 second leaf had its inception in a completely different organogenic 

 relationship. Are we to suppose that there is some abrupt change 

 in the developmental harmony and pattern as between leaf I and leaf 2, 

 and again between leaf 2 and leaf 3, whereas the development from 

 leaf 3 onwards is in conformity with a single pattern ? If we consider 

 the embryonic development in terms of an underlying biochemical 

 pattern, and not simply in terms of the visible morphological results, 

 many of the difficulties raised by these curious features in the embryo- 

 geny of O. moluccaimm disappear. In this view, there is developmental 

 harmony from the outset, as is common in embryos at large, and not a 

 series of somewhat unrelated developments as Campbell's interpretation 

 would appear to suggest. In the embryogeny of O. moluccamun, as in 

 O. vulgatum, the root is precocious, presumably in relation to the 

 nutrition drawn from the prothallus. Subsequently, possibly in relation 

 to the photosynthetic activity of the first leaf and uptake of nutrients 

 by the root, a more balanced metabolism supervenes and normal 

 morphogenetic activity at the shoot apex is thereafter maintained. 



In O. pendulum the young sporophyte is characterised by the 

 formation of a very large foot from the hypobasal segment, while the 



