Palaeontoloo^ie. 377 



^fe 



Vasculares; but while the prevalence of megaphylly is consistent 

 with the hypothesis of te origin of the sporophyte from a branched 

 thallus it is opposed to the view that the vascular sporophyte was 

 derived from a sporogonium. Professor Lignier's view that the 

 numerous simple leaves of some Sphenophylls, of the Calamites and 

 Equisetttj arose from highly Compound leaves, such as those oi Archaeo- 

 calamites and Pseiidoboniia, by subdivision and by the Separation 

 of the lobes as separate leaves is accepted. The anatomical gap 

 between Eqiiisetales and Sphenophyllales has been to a certain extent 

 bridged by the discovery of centripetal xylem in the Lower Carboni- 

 ferous Protocalamites. In the first edition, Bower's view that the 

 sporangiophore is an organ sui generis was provisionally adopted; 

 but as on actual evidence there is nothing to prevent our regarding 

 the sporangiophore as always foliar it seems unadvisable to multiply 

 further categories of organs; at the same time the differentiation of 

 the sporangiophore probably took place very early and the organ 

 may be of considerable morphological importance. Throughout the 

 Sphenophyllales they are the ventral lobes of the sporophyll, the 

 fertility of the dorsal lobes in Sphenophylluni fertüe being probably 

 a secondary modification. Though free from the sporophylls the 

 sporangiophores are probably their displaced ventral segments. Recent 

 Eqiäseta are regarded as reduced from larger forms. A rather 

 detailed account shows that the relation of the stalked synangium 

 of the recent Psilotacene to the subtending leaf or bract is essentially 

 the same as that obtaining between sporangiophore and bract in 

 the Sphenophyllales. In the present edition the Lycopsida are 

 regarded as much more remote from the Sphenophyllales than they 

 were in the first. The latter were probably derived from mega- 

 ph^^lous tj'pes and were sporangiophoric, whereas though the 

 Lycopods may have been descended from large-leaved forms and 

 though the absence of a specialized sporangiophore in them may be 

 due to reduction there is no evidence for this. Probably the afhnity 

 between Lycopods and SpJienophylls is not closer than that between 

 the Sphenopsida and Fenis. Among Lycopods Selaginella is regarded 

 as not nearly related to Lepidodendron, though Isoetes may have some 

 connection with the latter. As regards the Pteropsida, the Botry- 

 opterideae, while not on the direct line of descent of the recent 

 Penis or of the Pteridospernis, yet have some affinity with these, 

 particularly with the Ophioglossaceae which they perhaps approach 

 more closely than do any other plants known to us. As the Ophio- 

 glossaceae are descended from primitive Ferns the forms with well 

 developped leaves are on the whole more primitive. The majority 

 of the Lower Carboniferous Fern-like plants were probably Pterido- 

 sperms. The stele of Cladoxylon may have been derived from that 

 of such a type as AsterocJilaena. SiitcUjfia shows that polystel}' arose 

 within the Pteridospermous family to which that genus belongs. As 

 no heterosporous Palaeozoic Fern is known the gap between the 

 Ferns and the allied seed-plants is a wide one; Mr. Kidston's view 

 that the Pteridosperins and Ferns of the Marattiaceous type had a 

 common origin is well founded and not inconsistent with a relation 

 between Pteridosperms and Botryopterideae, since possible links occur 

 between the latter order and the Marattiaceae. The Pteridosperms 

 are to be regarded as a vast plexus of which but few types are 

 known. The Calamopityeae are regarded as a series parallel with 

 the Lyginodendreae and are of great antiquity. The Cycadoxyleae 

 may have sprung from the Lyginodendreae and ma}'^ have been 



