474 OPHIOGLOSSALES 
only be held as the representatives, secondarily reduced, of leaves primitively 
expanded above ground. 
Another feature for comparison is the balance between the root and 
the shoot. Owing to the saprophytic mycorhizal habit of the prothallus 
—and in some of the species even of the sporophyte itself—there is no 
immediate need for leaf-expansion, though an effective root-system is 
wanted, especially where it is itself mycorhizic. This finds its realisation in 
the embryogeny ; for the root-development in the Ophioglossaceae is liable 
to be hurried forward, and the development of the shoot to be postponed. 
That is seen in O. vulgatum, where the first root may already have freely 
emerged from the prothallus even before the shoot is clearly initiated. 
B. Lunaria also shows the first root as predominant, and the shoot relatively 
backward in development, with its succession of scale-leaves. Both these 
familiar plants are thus relatively specialised types of their respective genera. 
But the case of O. pendulum shows a still more extreme type; and it 
seems not improbable that the precocious development of the root has 
completely upset, the balance of parts in the embryo, with the result that 
the primary axis and cotyledon are difficult to locate, or may be even 
entirely arrested. Comparing the embryos of the family as a whole, 
it would seem probable that the primitive prothallus was above ground, 
and that in the original state of the seedling even the first leaf was an 
effective assimilating leaf, while those with one or more ineffective scales 
show a more advanced adjustment to their underground habit. The 
deferring of the period of functional activity of the shoot carries its 
reflection back to the early steps of the embryogeny; the relatively 
late appearance of the axis with its appendages is thus explained, as wel. 
as the apparently precocious development of the root. .The differences in 
these respects shown by the various representatives of the family indicate 
their unusual capacity for adjustment of such details. It is through con- 
siderations of this nature that we may bring these embryos into relation 
with those of other Pteridophytes where the embryo shows differentiation 
at an earlier stage. 
The late differentiation of the parts of the embryo in the Ophioglossaceae 
brings with it a difficulty in their exact location relatively to the primary 
segmentations of the zygote. There is no doubt that in the types under 
consideration (excluding the type of B. odguum), the apex of the axis 
arises in them all from the epibasal hemisphere, and allowing for distortions 
due to unequal growth, it appears to be coincident with, or in near 
proximity to, the intersection of the primary octant-walls. Thus as regards 
the initial polarity the Ophioglossaceae resemble other types of Pterido- 
phytes. The cotyledon appears in close relation to the apex of the axis, 
both in time and space, and it usually lies between the apex of the axis and 
the first root: but it will be remembered that in Jsvefes, which offers some 
other points of analogy, the root is on the opposite side of the axis to the 
cotyledon.” As to the exact point of origin of the first root there is some 
