446 OPHIOGLOSSALES 
Helminthostachys. Such a difference is of common occurrence within near 
limits of affinity. For reasons given in Chapter XVI. the upright radial 
type will be held to be the primitive, and the dorsiventral as seen in 
Helminthostachys the derivative: it is interesting to note that this goes 
along with a large and heavy leaf-development. 
While, however, there may be no doubt of the homology of the spike 
in all the three genera, it is to be noted that the level of its insertion 
upon the adaxial face of the sterile leaf is not constant. In most species 
of Ophioglossum, as also in Helminthostachys, it is at the base of the 
sterile lamina; but in O. Bergianum, where there is no differentiation of 
petiole and lamina, it is but a short distance above the insertion of 
the leaf itself upon the axis. In O. palmatum it has been seen that the 
numerous spikes may be distributed over a considerable length of the 
basal region of the lamina. In Botrychium the differences in respect of level 
of insertion are more marked: in B. Zunaria it is usually a short distance 
below the lowest pair of pinnae: in ZB. fernatum it may be about four 
inches below them, and about two inches from the base of the frond: 
in B. dauctfolium the insertion may be close to the base of the frond; but 
in B. virginianum, on the other hand, it may be above the second pair of 
sterile pinnae. The chief question in the morphology of the Ophio- 
glossaceae will be as to the real nature of this member, which shows so 
variable a level of insertion, though it maintains in a remarkable degree 
its constancy of character, as well as its position upon the upper face of 
the leaf. A knowledge of its development and internal structure will be 
essential before arriving at any definite conclusion. 
Lastly, in comparing the shoot of the Ophioglossaceae as a whole 
with that of the strobiloid types, the essential relation of leaf to axis is 
the same. The nearest resemblance as regards general proportion is with 
Tsoetes, both having the sttinted axis and spiral arrangement of the relatively 
large leaves: one main difference lies in the tendency to the monophyllous 
habit in the Ophioglossaceae, which may be held to be a consequence of 
its perennation underground. It has been seen that in Jsoe¢es all the 
leaves of the mature plant show evidence of being potentially fertile, but 
that an early abortion of the sporangia leaves some of them sterile. A 
similar abortion is seen in the Ophioglossaceae: in QO. vudgatum a rudi- 
mentary spike is often to be seen on apparently sterile leaves, as a small 
peg-like growth in the place where the normal spike would be inserted: 
it is shown in Fig. 235, letter z In other cases it may be found 
that no vestige of the spike remains. Similar abortive spikes have been 
seen in O. reticulatum and pendulum. In Botrychium Lunaria and simplex 
extraordinarily small plants are found to bear fertile spikes, porportional 
in size to the sterile lamina; but in some cases of small, weak plants 
the fertile spike appears to be entirely absent. In Me/minthostachys Lang 
observed that abortive fertile spikes are commonly found, subtended in 
each case by a fully developed sterile lamina. It thus appears that the 
