The Present Position of Palaeozoic Botany. 147 



The characters on which Prof. Jeffrey mainly relied as dis- 

 tinguishing his two main groups are three : the Lycopsida are typically 

 microphyllous, the Pteropsida megaphyllous ; the Lycopsida are "clado- 

 siphonic", the Pteropsida ''phyllosiphonic", i. e. the hollow vascular 

 cylinder (when present) is interrupted in the former only by the 

 exit of branches, forming ramular gaps, in the latter by the exit of 

 leaf-traces, forming foliar gaps ; lastly, the Lycopsida are characteristi- 

 cally strobiloid as regards their fructification, while in the Pteropsida 

 strobili only appear in the higher members of the division (Phanero- 

 gamia). These characters are by no means constant, and are open to 

 much criticism; the general grouping has, however, sufficient claims to be 

 a natural one, to afford at any rate a basis for the discussion of affinities. 



We may graft on Prof. Jeffrey's arrangement a proposal of 

 Prof. L i g n i e r ' s to associate the Sphenophyllales and Equisetales in 

 the sub-division Articulatae. So far then as concerns the groups 

 which we have to consider in this article, our provisional classi- 

 fication may take the following form: — 



Lycopsida 



Sphenophyllales \ ^rtie^iatae. 

 Equisetales ) 



Psilotales 

 Lycopodiales 



( 



Filicales 

 eridosi 

 mnospermeae 



Pteropsida Pteridospermeae 1 ^ , ^ 



^ ) Sperm ophy ta. 



The Psilotales, though without authentic Palaeozoic representatives, 

 are included in the list because it is necessary to discuss their 

 affinities in the light of palaeontological data. 



The composition of the Vasculares in Palaeozoic times was thus 

 widely different from what we find in the recent Flora, not only as to 

 the groups represented but also as to their relative importance. The 

 Pteridophytes and the lower Seed-plants then had the field to them- 

 selves, and shared among them all the leading roles in the vegetable 

 world, filling a place which has since, for the most part, been taken 

 over by families of more modern origin. Groups of plants which now 

 play an altogether subordinate part, or have disappeared altogether, 

 were then richly represented, and in many cases showed a far higher 

 and more varied organization than is found among their nearest allies 

 in later times. 



In considering the evidence we possess as to the vegetation of 

 Palaeozoic ages it is necessary to bear in mind that our knowledge 

 is to a great extent limited to floras of a very special kind. The 

 Palaeozoic plants known to us are for the most part, though not of 



10* 



