124 Scientific Proceedings, Royal Dublin Sociehj. 



sporangia, as first noted by Kidston, are not uncommou. The general 

 impression one gets from the examination of a number of fertile fronds is 

 the absence of a sharp demarcation between the vegetative and reproductive 

 regions. The condition is such as one might expect in a primitive type, and 

 is occasionally met with in living Ophioglossacese. 



The fertile pinnule stands out almost at right angles to the axis of the 

 secondary rachis of its pinna and is 1-2 cm. long. It is, though more or 

 less filamentous, not reduced to a midrib or median nerve, as stated. The 

 transformed pinnule is traversed along its whole length hy several vascular 

 bundles, which enter from the secondary rachis. These are well seen in its 

 general substance, and also in its slightly expanded process-like vegetative 

 tip, which is often branched (Pis. IV. and VI.). This fertile pinnule, hitherto 

 known as the sporangiophore, may be called the sporophyllule. It was 

 probably, when alive, green throughout its length, and capable, especially 

 at its free end, of carrying on a little photo-synthesis. It is important not 

 to overlook the presence of this vegetative tip, since Schmalhausen's separation 

 of tlie species Archceopteris archetypus is partly based on the presence 

 of a sterile tip of the lamina in it and its alleged absence in A. hibernica. 

 Nathorst finds little evidence in Ellesmere Land material of the conspicuous 

 sterile tip of A. archetypus, figured by Schmalhausen in his Russian specimens. 

 On the other hand, I have rarely seen a fertile pinnule of A. hibernica in 

 which a sterile, usually branched tip, is not present. Thus the complete 

 restriction of the sporophyllule to a purely reproductive function is a rarity 

 in A. hibernica. The sporophyllule gives rise on its upper surface to a hori- 

 zontal row of six to twenty, more or less fusiform or claviforni sporangia 

 2 or 3 mm. in length, each on its own short stalk. The sporangia are only 

 rarely biseriately arranged as Zeiller describes them. It is only occasionally, 

 too, that the sporangium is sessile, or that two or three are borne together on 

 the same stalk. Schimper's figure shows a general racemose arrangement 

 of the sporangia which is not observable in our Irish specimens. Confusion 

 has, no doubt, arisen owing to the crowded, crushed character of the fertile 

 pinnules in the slab of rock in some cases. It is when the sporophyllule has a 

 less reduced surface that the sporangia maj' be seen arranged on it in two 

 rows and spread out like a marginal fringe on either side of it. Though the 

 sporangia are normally borne on the upper or adaxial side of tlie pinnule, 

 their free ends are often directed downwards, owing to the backward curva- 

 ture of the pinna and pinnule. The sporangia may thus often appear 

 pendulous and hang downwards as really as in the Pteridosperm genus 

 Crossotheca, in which the truly pendulous microsporangia arise on the under- 

 side of their expanded sporophyll-segments. In such an arrangement the 



