The Filicinean Vascular System. 31 
Professor Jeffrey, as is well-known, has proposed to divide the 
Pteridophyta into two primary groups: the Lycopsida or palin- 
genetically microphyllous forms, in which the departure of the 
leaf-trace does not leave a gap in the stele, and which includes all 
the phyla just mentioned ; and the Pteropsida or palingenetically 
megaphyllous forms, in which the departure of the leaf-trace does 
leave a gap in the central cylinder when this is siphonostelic in 
structure, and which includes the Ferns, Ophioglossales, Pterido- 
sperms, Gymnosperms and Angiosperms. “ These two great 
stocks ” says Jeffrey, “ appear to have been separate back to the 
beginning of the period when the palaeontological record begins” 
(’02, p. 144). This statement, with certain qualifications, is no doubt 
true, but nevertheless the grounds of the fundamental distinction 
proposed by Jeffrey appear open to a certain amount of criticism. 
In the first place the evidence now rather tends to the 
conclusion, as was pointed out in the first lecture, that many of the 
modern microphyllous forms are reduced derivatives of mega¬ 
phyllous ancestors. At any rate it is a striking fact that a large 
number of the Palaeozoic forms had dichotomously branched leaves. 
Whether or no the Ferns have any direct connexion with these 
forms is another matter, but the supposition that the “ Lycopsida ” 
are all palingenetically microphyllous is certainly an assumption 
which lacks justification. 
With regard to the anatomical distinction, there seems to be 
no escape from the view that the anatomical relation of leaf-trace 
and stele must depend first upon the actual size of the leaf-trace in 
relation to the stele, and secondly upon the construction of the stele 
itself. The departure of the small leaf-traces from the stele of a 
Lycopod or of a Sphenophyllum leave no gaps in the stele, whether 
the xylem of the latter is solid or medullated ; in the latter case 
because they are too small to affect the whole breadth of the 
xylem ring. 
Professor Jeffrey has nowhere discussed in detail the origin of 
the siphonostele from the protostele, though he himself (’98) stated 
the view of the primitiveness of protostely. In the Gleichenia — 
Lindsaya—Wibelia series (LecturesI V & V) the origin of phyllo- 
siphony certainly goes hand in hand with the origin of solenostely, 
but in the Osmundaceous series discovered by Kidston and Gwynne- 
Vaughan the origin of a hollow stele is clearly shown to be 
unconnected with phyllosiphony. 
In the medullated Lycopsida, as has been said, the departure 
