180 Scientific Proceedings^ Royal Dublin Society. 



several other parts of his invahiable work on the Bear Island Flora, Nathorst, 

 as I learnt by correspondence, uses the word " Mittelader " when intending to 

 use " Aderung.") Sphenojjteris Rookeri has a well-marked venation, witli 

 no sign of a midrib, and is distinct from our plant, in which no venation is 

 observable. Through the kindness of Professor Nathorst I have received a 

 specimen of his very rare Sphenopteridium Keilhaui, and have thus been able 

 to compare it with Forbesia. I can see nothing in S. Keilhaui of the 

 cancellous character of Forbesia, which has too a more pronounced dichotomous 

 character than S. Keilhaui, with its keeled axis, indicative of vascular tissue. 

 In both species, as well as in Oephalopteris mirabilis, Nath., Rhacophyton cun- 

 drusorum, Cr^pin, S. Lebedewi, Schmalhausen, S. flaecida, Crepin, and similar 

 early Palaeozoic forms, the leaf-lamina is but little pronounced, and looks as if 

 it were in the first stages of emergence by the flattening out of the ultimate 

 ramification of a branching ribbon-like axial system. 



Forbesia is thus a veinless plant, though found, so far as Ireland is 

 concerned, in a later formation than that which gives us the vascular 

 Sphenopteris Hookeri. Sooner or later it will, I think, be recorded for the 

 Devonian rocks too. It must be remembered that we are now re-examining, 

 under the inspiration of recent palseobotanieal discoveries, material collected 

 in 1851 and left unexamined, owing to insufficiency of staff, until 1864 (by 

 which time much of it had been lost or dispersed, says Jukes, (op. cit.). The 

 early Palseozoic flora of Ireland is one of the most interesting and illuminating 

 in the world, and urgently needs further investigation. 



The sclerotic framework mentioned is not a surprising feature. Though 

 the leaves were small, they needed support, and this the sclerotic bands would 

 give, just as in Heterangium Grievii, with its small leaf -segments, the sclerotic 

 plates supplement the vascular tissue. The chambered tissue suggests a 

 marshy or semi-aquatic habit for Forbesia. More interesting still than the 

 absence of vascular bundles is the lack of structural differentiation of axis 

 and frond. Except for the flattening out of the leaf-segments, there is no 

 marked difference between axis and frond. I interpret this as indicating that 

 Forbesia represents a primitive form in which the plant-body is nearer than 

 any yet unearthed to the hypothetical ancestors of the Pteridophyta, i.e., to 

 a form, comparable with the " Prohepatic " of Lignier (5), in which tlie 

 plant-body is still more or less in the thallus state. Such a form shows no 

 differentiation into stem and leaf and no vascular tissue, but is dichotomously 

 divided. In its next stage it begins to erect itself and to give off flattening 

 branches of the thallus which will gradually become leaves. The line of 

 connexion of the Pteridophyta with the non-vascular cryptogams cannot, 

 I think, be sought through theMusoi, which bear a relation to the Pteridophyta 



