Stiles . — The Podocarpeae. 505 
importance of the ovule as compared with the sporophyll has already been 
suggested by Mr. R. B. Thomson, 1 and by Mr. Brooks and the writer. 2 
The vascular supply of the microsporophyll of the Podocarpeae is 
just the same as that of the Lycopodiales as far as its distribution is 
concerned. 
As regards vegetative organs further evidence in support of the view 
under discussion is derived from a consideration of the leaves. The 
characteristic of the leaves of living Lycopods and many of the fossil ones 
is their relative smallness and their possession of a single median vascular 
bundle. Arguments have been advanced already in the course of this paper 
to show that the primitive type of coniferous leaf was the common uninerved 
type characteristic of all Conifers except a few Araucarieae and the Nageia 
section of Podocarpus. Some single-veined Araucarian leaves, it is true, 
have probably been reduced from broader leaves, 3 but there is no evidence 
of this in the leaves of any of the Podocarpeae or of any other order. The 
slight tendency to form wider leaves with parallel veins, as exhibited in 
Agathis and Podocarpus § Nageia , may be compared with the still slighter 
tendency to the same thing in Sigillaria , where in some species ( Sigillari - 
op sis) the leaves were traversed by two parallel veins. 4 
The presence of leaf-gaps in the stele of the Coniferales has been 
regarded by some botanists as affording important evidence in the considera- 
tion of the origin of the Conifers. This line of argument was first used by 
Professor Jeffrey in 1902, when he inferred that the Coniferales were 
descended from the Fern-plexus on the ground that foliar gaps occur in 
the stele of both these groups, but are absent in the Lycopodiales. 5 Coulter 
and Chamberlain regard this argument as a very strong one, for in discussing 
the objections to Seward and Ford’s view of the Lycopodialean origin of 
the Araucarieae they say: ‘Perhaps the most fundamental objection is the 
presence in araucarians of foliar gaps and of wood indistinguishable from 
that of Cordaitales.’ 6 
It is clear that this objection is based on the assumption that the 
presence or absence of leaf-gaps in the stele is a character fixed and 
unalterable in the phylum, an assumption for which, although it is so 
generally accepted as a fact, there is no supporting evidence. There 
certainly is evidence that in the evolution of the Lycopodialean vascular 
system, just as in the Cycadofilices, 7 one of the most important tendencies 
was the elimination of primary centripetal wood. Thus Dr. Scott remarks, 
‘ A gradual transition may be traced from the protostelic type, through the 
medullated forms of Lepidodendron and the ribbed Sigillarias, to the smooth- 
barked Sigillarias, in which the ring of wood separates, more or less com- 
1 Thomson (’09 2 ) p. 351. 2 Brooks and Stiles (TO), p. 314. 
3 Seward and Ford (’06), p. 350. 4 Arber and Thomas (’08), p. 148 ; Scott (’09), p. 230. 
5 Jeffrey (’02), p. 119. 6 Coulter and Chamberlain (TO), p. 31 1. 7 Scott i/02), p. 25. 
