THE SPORE-PRODUCING MEMBERS 701 
annulus is the last representative. A somewhat similar condition appears 
in Ophioglossum simplex, where the spike is present, but the subtending 
leaf absent (p. 441); in both cases the structure seen appears to be based 
upon the persistence of the sporangiophore, while the leaf is abortive—in 
fact, the converse of the process which brings the ‘“Selago” condition 
into existence. 
There remain, however, certain instances where the distinction between 
the leaf and the spore-producing members appears to break down, and 
middle forms appear with the characters of leaves bearing sporangia; the 
annulus of Egucsetum sometimes bears sporangia, grouped as upon mal- 
formed sporangiophores (p. 382); or sporangia may appear upon the sterile 
leaf of Botrychium (Fig. 242, p. 443); or, as in Sphenophyllum fertile 
(p. 404), the bract bears sporangia as well as the sporangiophore which 
it subtends. I do not think that these occasional exceptions suffice to 
prove that leaves and sporangiophores belong to the same category of 
parts, any more than the substitution of a foliage leaf for an ovule, in 
certain well-known cases, proves that the ovule is really an organ of the 
same category as the leaf. What they really appear to show is, that in 
certain cases a primordium is not always of clearly defined character at 
its: initiation, and consequently that the characters pertaining to members 
of distinct category may occasionally be intermingled. Accordingly, not- 
withstanding the exceptions quoted, the distinction of leaves and sporangio- 
phores may be upheld for the early forms of Pteridophytes. 
It thus appears that the whole plant-body, as seen in the simpler 
Vascular Plants, is referable to the simple shoot or strobilus, of radial 
construction,’ as a unit; that it consisted, in its most primitive form, of 
an unbranched axis, simple leaves, and unilocular spore-producing members, 
all of which were distinct in their character and in their phyletic origin, 
and none the result of metamorphosis of another part; that the whole 
plant-body of the known Pteridophytes may be regarded as derived from 
some such simple source, by continued apical growth, and terminal and 
adventitious branching of the axis, and by branchings and fissions of the 
appendages ; by adoption of a dorsiventral in place of the primitive radial 
habit; by abortion of certain of the spore-producing members, which 
differentiated the sterile regions from those which remained fertile; and 
in these sometimes by abortion of the leaves themselves, thus leaving the 
spore-producing members as the sole appendages. Such an origin is fully 
in accord with thé details of individual development; for the ontogeny 
often demonstrates those very progressions from the simpler to the most 
complex state which the phyletic development of the more elaborate forms 
from so simple a source would require. 
Combining the results which thus follow from the detailed examination 
of Vascular Plants with the conclusions from comparison of the Bryophytes, 
there appears to be very strong support for our general theory of 
origin of the sporophyte, as the essential constituent of the Flora of the 
