COMPARATIVE DISCUSSION 479 
among themselves—and not giving undue weight to the species which 
happen to be the commonest—leads almost inevitably to their seriation 
in the way indicated above (pp. 43 1-446). The upright radial, unbranched 
shoot is the central type, and the only departure from it is in the 
large-leaved Helminthostachys, where the dorsiventral rhizome may be held 
as illustrating a secondary condition; the primitive stock was probably 
upright and radial for them all. It was also polyphyllous, as in most 
other Vascular Plants, while each leaf bore the characteristic spike, which 
is essentially identical in them all, whatever its actual nature may be 
held to be. Within the family it is probable that the three genera 
illustrate three distinct lines of descent from some common source, already 
- provided with a body of the nature of the spike. In Ophioglossum the 
original polyphyllous state is still seen in various smaller species: and it 
is worthy of remark that the nearest similarity to other strobiloid types is 
seen in those species in which the appendages are simplest and smallest. 
But, as pointed out above, the monophyllous habit has biological advan- 
tages in plants with an underground stock, and with its adoption followed 
enlargement of the individual leaf, and of the spike, the two parts showing 
some degree of parallelism of dimensions. Thus the ordinary type of 
O. vulgatum is attained. Fission or chorisis of the spike is an occasional 
occurrence in O. wulgafum and other species, but it became a fixed 
character in O. palmatum. It appears probable, however, that it is only 
attained in this species in fully matured plants: thus the individual of 
this species may be held to illustrate in its own life the origin of its 
more complex form. Here again a parallelism exists between the irregular 
lobing of the sterile lamina and the number of spikes which it bears. It 
would be difficult to explain these characters in any other way than as an 
ascending series involving chorisis. A probable ‘line of reduction does, 
however, occur: it is illustrated by the series O. pendulum, intermedium, 
and stmplex, the latter having no functional representative of the fertile 
lamina. 
A distinct line, also of progression, is seen in Botrychium, but with 
different details. The series of forms seen in 2. simplex (Fig. 240), and 
in the young plants of &. Lunarza, link on by their simplest forms with 
the condition of a small Opsioglossum with simple sterile lamina and 
unbranched spike: by very gentle gradations they lead on to the branched 
sterile lamina and fertile spike characteristic of the genus, the branching 
of the spike being closely connected with the enlargement and fission of 
the sporangia. There is reason to believe, as Luerssen has indicated, 
that these forms illustrate progress in the life of the individual, from the 
simpler to the more complex: and the suggestion lies near to hand that 
the individual in this respect ‘climbs up its own evolutionary tree.” The 
continuation of this method of advance would lead onwards to the' most 
complex forms, the spike and lamina preserving a parallelism as before. 
‘Rab, Krypt. Flora, iii., p. 579. 
