1-32 Scientific Proceedings, Uoyal Dublin Socieip. 



represented by Ephedra ; and Drude, in the course of the discussion, 

 suggested that, as a farther step backwards, the condition of things in Equi- 

 setum was worthy of note. No palaeontologist took part in the discussion ; 

 but it was interesting to hear afBuities suggested between types represented 

 by these genera. 



In the warm, moist atmosphere, rich in carbonic acid, of the Upper 

 Devonian epoch,' plants throve, and some produced large, divided leaves, 

 carrj'ing, in not very sharply-defined regions, the reproductive organs. Under 

 less luxuriant conditions, though the same principle of division of labour 

 remained, the bipinnate frond was reduced to a simple or divided lobe, with 

 an attached or fertile lobe, in which the sporangia were crowded. Later, as 

 reproduction became more specialized, the fertile lobe became heterosporous, 

 and branching now occurred in the reproductive instead of in the vegetative 

 organs, giving us flowers of two kinds, each with its own sporangia. The 

 addition, or not, of a jDerianth to each flower, and the conversion of tlie spathe 

 into an organ attractive in pollination, would give a further stage in the 

 evolution of the Aroidese. Bugler states, though naturally not in this 

 connection, that 92 per cent, of the Aroidese are tropical plants, and that, as 

 they are found growing mostly in moist habitats, where they rapidly decay 

 when dead, it is not surprising that they are little known in the fossil state. 



Are we now in a better position than formerly to decide as to the 

 afBuities of Archeeopteris ? 



Our discussion is still crippled by the absence of information on its 

 internal anatomy. We have carbonaceous casts or impressions only to 

 aid us, and thus the evidence is incomplete. It will be useful to consider 

 the various characteristics of Archseopteris seriatim : — 



1. The "fern-like " bipinnate frond is found in Pteridosperms as often 

 as in ferns. 



2. The dichotomy of the frond and its pinnae is common in Pteridosperms 

 and in certain groups of ferns. 



3. The aphlebioid pinnules occur in Pteridosperms, and in ferns. 



4. The stipules are like those of Angiopteris, but came away with the 

 frond from the parent plaut. In the Marattiaceee, as Nathorst notes, they 

 remain attached to the leaf-base on the parent plant. Stipules are known in 

 the Cycadese, though Wieland gives very little attention to them in his 

 recent fine work on the Cycadoidese. 



' See Chambei'lin and Salisbury : Geolog)', vol. ii, p. 603, where another view of the climate is 

 also given. 



