290 Bower . — Notes on the Morphology of 
criterion of pinna-nature within this family, for the supply both to spikes 
and to pinnae may be intramarginal. It may then be doubted how far 
a mere marginal origin of the vascular supply can be used as a criterion of 
pinna-nature, as Dr. Chrysler does in the present case. It cannot be accepted 
as outweighing other considerations, such as arise from comparison based on 
a large series of specimens. 
VII. It has been shown that the vascular supply to the median spike 
in the leaf examined in 1904 consists, like that of the succeeding two spikes, 
of three strands, of which the median one is the largest. All the three 
spikes are in fact equivalent in this respect (Fig. 17, 1 -IX). Dr. Chrysler’s 
suggestion on the basis of the vascular connexions alone is ‘ that the lowest 
spike in this specimen represents two fused lobes of the leaf, while the next 
two spikes represent single lobes \ The fact that the vascular supply to all 
of these is equivalent in all except the source, being in the one case median, 
in the others marginal, should carry some weight with vascular anatomists, 
raising a doubt of the validity of the conclusion. The vascular supply to 
two fused pinnae might be expected to be more complex than that to 
a single lobe. On the other hand, the structure actually observed is such 
as might be expected on a theory of pleiogeny. 
VIII. The species which show the peculiarities under discussion belong 
to the two sections of the genus generally admitted to be specialized. It is 
in such forms that one may most readily expect developments which will 
diverge from the usual type and follow a line of their own. Both species 
are partially saprophytic, a condition often associated with unusual develop- 
ments, reducible with difficulty to the ordinary schemes of construction. 
In plants biologically so restricted as these half-saprophytic dwellers on 
decaying trunks and humus a large spore-output is almost a necessary 
condition of survival, or at least of spread. This utilitarian reason for 
amplification is easily intelligible, and the ready means appears to have 
been amplification and irregular lobing of the sterile lamina, and repetition 
of the fertile spike. Both ot these were probably special and phyletically 
late occurrences. There seems to be no reason to hold that they should 
necessarily be retrospective developments. Dr. Chrysler appears to assume 
that they were. I have suggested, on the other hand, that both the sterile 
and the fertile regions of the leaf have progressed along new lines of 
development, and that their parts are not necessarily reducible to terms of 
pinnae such as are seen in the pinnate members of the family. 
The conclusion arrived at may be summed up as follows. The spike 
of Eu-Ophioglossum is regarded as the unit upon which further develop- 
ment has played. The facts, both developmental and anatomical, fall in 
readily with a theory of amplification of that unit, or pleiogeny, as explain- 
ing the complex forms observed in O. pendulum , and more pronouncedly 
in O. palmatum . The sterile lamina enlarged and formed irregular lobes. 
