COMPARATIVE DISCUSSION , 489 



more active development in Botrvfliium finds its correlative in the more 

 active thickening seen in Sphenophyllum. These again may be mere 

 analogies, but they are cumulative, in that they run parallel with others. 



Lastly, it has already been shown that as regards structure of the 

 roots there are unmistakable points for comparison of the Ophioglossales 

 with the Lycopodiales on the one hand, and on the other with the Fili- 

 cales, especially the Marattiaceae : the former comparison is in respect 

 of the simpler, monarch types, the latter as regards the more complex: 

 the latter branch monopodially as a rule, behaving thus like the roots 

 of the Filicales : the monarch roots, however, show dichotomous branching. 

 Unfortunately, the Psilotaceae, which show so many other points for com- 

 parison, are rootless, while the roots of Sphenophyllum are so imperfectly 

 known as to give little help. Though the facts relating to the roots are 

 not in any way decisive, they indicate, what emerges from so many other 

 comparisons, that Ophioglossum shows characters approaching the strobi- 

 loid Pteridophytes, while Helminthostachys compares rather with the Filicales, 

 and Botrychium takes a middle position. 



In the embryology two distinct types have been recorded for the 

 Ophioglossaceae, the one with and the other without a suspensor. That 

 without a suspensor corresponds in its essentials to the type prevalent 

 in those Pteridophytes which have the usual octant division. But there 

 are modifications here in accordance with the underground origin from 

 a large mycorhizic prothallus, which nourishes itself saprophytically : the 

 chief of these is the deferring of the period of functional activity of the 

 shoot : consequently it is differentiated late, and though the root is not 

 initiated early, as compared with other embryos, it very markedly precedes 

 the appearance of the axis and cotyledon in Ophioglossum, and in less 

 degree in Botrychium. This appears in an extreme form in those species 

 described by Campbell, and especially in O. pendulum, where it is possible 

 that the primary shoot is permanently replaced by adventitious root-buds, 

 similar to those common in the genus. These modifications in time of 

 development make the reference of the parts to definite positions in the 

 embryo somewhat difficult. But it seems certain, nevertheless, that in the 

 less extreme forms the axis arises from the epibasal hemisphere, in close 

 proximity to the intersection of the primary octant-walls. The cotyledon 

 appears between the stem-apex and the root, but it is late in origin. In 

 0. vnlgatum it appears simultaneously with the axis, and the relation is 

 so close in B. virginianum that Jeffrey states that the cotyledon, like any 

 other leaf, is derived from the shoot meristem. This is interesting in 

 its bearing on the theory of the cotyledon, which has been held to be 

 simply a leaf of the shoot showing anticipatory development (see p. 186-7). 

 The foot which is not largely developed originates from the hypobasal 

 hemisphere. The position of the first root appears to be indeterminate, 

 as it is in some other embryos, a fact which is interesting as upholding 

 the view that it is a mere accessory to the shoot. It is referred by 



