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 Equisetum 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 the 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 



