33 
Anatomy of the Ophioglossaceae. 
met with. The apical pole of the embryo with a suspensor always points 
away from the archegonial neck, but the position of embryos without 
suspensors exhibits differences. The position of the embryo (as compared 
with embryos with suspensors) may be completely inverted, the epibasal 
pole being directed towards the archegonial neck instead of away from it. 
This is the position of the embryo of Equisetum , which has no suspensor. 
It is found in Isoetes in contrast to the embryos of other Lycopodiales 
where suspensors are present. In the Ophioglossaceae similarly, and even 
in the single genus Botrychium , embryos with and without suspensors are 
met with, and inversion of the polarity of the embryo is associated with the 
absence of a suspensor. From the evidence afforded by the Lycopodiales 
and Ophioglossaceae, Bower regards the type of embryo with a suspensor 
as the more primitive and as having been associated with a bulky prothallus, 
often subterranean and saprophytic. It appears to be implied, though not 
actually stated, that the suspensor is here biologically useful in carrying the 
embryo deeper into the bulky prothallus. The non-development of the sus- 
pensor and the associated inversion of the embryo are regarded in both of these 
groups as having been an advantage in avoiding an ‘ awkward curvature ’ and 
simplifying ‘ an awkward and inconvenient process \ The type of embryo 
without a suspensor is regarded as c characteristic of stocks with less bulky 
prothalli, usually above ground and self-nourishing Whether a similar 
progression from embryos with to those without suspensors has taken place 
in the Filicales (excluding the Ophioglossaceae) and the Equisetales is left 
an open question by Bower, but the progress from more bulky to less bulky 
prothalli in the Filicales regarded as consistent with such an assumption. 
Thus we have as further generalizations (in addition to the primary 
one of the constant position of the apex of the shoot at the centre of the 
epibasal pale) : (a) the probability that the type with suspensor is relatively 
primitive ; (b) that the presence of a suspensor is correlated with more 
bulky prothalli ; (c) that the loss of the suspensor on inversion of the embryo 
may be regarded as a biological advantage. 
Since the date of publication of the ‘ Land Flora ’ our knowledge of the 
embryology of the Filicales has been increased by a fuller account of the 
embryos of Marattiaceae (including the embryo of Danaea } which is pro- 
vided with a suspensor) and by the main facts for Helminthostachys described 
in the preceding pages. The existence of forms with and without suspensors 
in two comparatively narrow circles of affinity, such as the Ophioglossaceae 
and the Marattiaceae, is of great interest. The interest is increased by the 
probability that both groups are relatively primitive among the Filicales. 
It thus appears most profitable to confine this discussion to the Filicales, 
and to critically consider the generalizations reached by Bower as applied 
to this phylum. In doing so it will of course be clear that all the facts for 
1 Campbell, loc. cit., pp. 142-6. 
D 
