EMBRYOLOGY 473 
base, and maintains that position as the growth proceeds. This is 
susceptible of no other interpretation than that a suspensor is formed, and 
that the whole embryogeny is inverted, as compared with that of other 
Ophioglossaceae where a suspensor is absent. The importance of this 
lies in its bearing on the general comparison of embryos, and on the 
estimate of the weight to be attached to some of those differences which 
have hitherto been made to bear a burden of comparative and phylogenetic 
argument. If we see that within a narrow circle of affinity the suspensor 
may be present or absent, and the apex of the embryonic axis be 
directed either towards the archegonial neck or away from it, then 
such characters become suspect. This will find 
its special application in the comparative study of 
the Lycopodiales and of the Ophioglossales. 
In the third genus, Aelminthostachys, the 
youngest stages have not yet been seen: but the 
old embryo resembles that of Botrychium virg?- 
nianum+ Jt has a large foot derived from the 
hypobasal region, while the primary root, first leaf, 
and stem-apex appear to be referable to the 
epibasal half. The first leaf has a ternate lamina, . 
and reaches the light, but the young plant remains 
attached to the prothallus till several leaves have \ 
been formed: one root lies below each of the 
earliest leaves, but in the older plant this regularity 
is lost (Fig. 267). An endophytic fungus is present 
in the first few roots, though the adult plant is 
normally free from mycorhiza. 
The character of the prothallus, and perhaps Gee ees eee oe 
also the position of the archegonium upon it, have ee Bistieal Site GREE 
to be taken into account when making comparison 
of the embryology of the Ophioglossaceae. All their prothalli are 
typically underground and saprophytic, and the embryos show differing 
degrees of adjustment to the peculiar conditions thus imposed upon them. 
In these facts the dominating features of the embryogeny may be found, 
and they must be borne in mind not only in any comparison with other 
Pteridophytes, but also as regards the. minor differences which they them- 
selves show. The most obvious points relate to the development of the 
earlier leaves: in Botrychium virginianum, Ophioglossum pedunculosum and 
Moluccanum, and in Helminthostachys the cotyledon itself may be expanded 
above ground ; but in both of the larger genera there are species which bear 
the first leaves as rudimentary underground scales: this is seen in O. 
vulgatum, where the second leaf only is effective for assimilation, and in 
B. Lunaria, where a succession of scale-leaves appear, and the eighth 
leaf is the first that is expanded above ground. The scale-leaves can 
Fic. 267. 
1Compare Lang, 2c. 
