686 CONCLUSION 
in the case of Lycopodiales (p. 337), Equisetales (p. 391), Sphenophyllales 
(p. 418), Ophioglossales (p. 464), and Filicales (p.646), how the stelar 
structure, however various, is uniformly referable in origin to the monostele : 
for it is seen in the young plant either to show a solid xylem-core, or a 
medullated state not far removed from that condition. The frequent 
occurrence of a like structure even in the mature axis of the early fossils 
has also been shown: and from such observations it becomes apparent 
how fully justified the opinion is that for the various types of the 
Pteridophytes the non-medullated monostele was the original vascular 
structure in the axis. 
It will probably be objected that in many of the Pteridophytes the 
embryogeny does not bear this out; and that what is apparent, especially in 
the larger-leaved types, is that the vascular tissue of the shoot is initiated 
by a simple foliar strand, which descends from the first leaf continuously 
to the root, and in fact that the axial system is in its origin little more 
than a sympodium of leaf-traces. But before this objection is allowed to 
have weight the condition in the smaller-leaved forms must be taken into 
account, and the question examined as a whole rather than from one aspect 
only. A comparison of those Lycopods, which are held to be relatively 
primitive, shows that the cauline stele is initiated in the first stages of the 
embryonic development; this is seen with particular clearness in Fig. 
190 C, D, E of Selaginella spinulosa, where the tissue formative of the 
stele can be recognised as extending up to the broad apex of the axis 
before any foliar strand is initiated. The same is the case in Lycopodium 
Phiegmaria (Fig. 185 c, D) and L. annotinum,) and it is indicated also 
in the imperfectly known embryology of Z. Selago (Fig. 183). -In 
these plants the vascular condition from the very first establishment 
of the embryonic shoot is the same as in the continued embryogeny 
(compare Fig. 172, p. 3g1): the stele is essentially cauline, and the 
foliar strands insert themselves upon its periphery. This appears to 
be the normal condition of small-leaved forms; according to our 
hypothesis these are themselves primitive, and the result of a com- 
parison of the embryogeny in the two types would be that in larger-leaved 
forms the cotyledon bulks more largely at first; that the axis in the first 
instance is correlatively reduced in size, and the cauline vascular core is 
reduced with it. But, nevertheless, the examination of the embryogeny 
has shown with constancy that the axis is pre-existent to all the other 
parts of the embryo, though it may often be correlatively reduced, or its 
development deferred where the cotyledon or the root is precociously 
developed. The same view will hold also for the constituent tissues of 
the axis, including the cauline vascular core. The condition where this 
xylem-core is present is accordingly held to be the primitive state of the 
embryo, that where it is reduced and even absent is held as the secondary 
and derivative. But even in the latter cases, the stelar tissue asserts 
1Bruchmann, Z¢., Pl. 4, Fig. 17. 
