27 
The Origin of the Pteridopliyta. 
It seems however reasonable to give at the outset a short 
summary of the evidence, other than anatomical, upon which my 
belief in the main idea common to the speculative views of 
Potonie', Hallier and Lignier is based, and my first lecture will 
therefore be devoted to this topic. 
I.—The Origin of the Pteridophyta. 
In dealing with an evolutionary question we have first to con¬ 
sider the datum or starting point from which the course of 
evolution to be discussed has proceeded. 
In the present case it is unfortunately impossible to do this 
except in the most speculative manner, the reason being that we 
we have no knowledge of the immediate predecessors of the plants 
which we know as ferns. The biggest gap in the plant-kingdom at 
the present time is undoubtedly that which separates the Pterido- 
phytes from the plants definitely below them in organisation, and 
directly we try to step behind the Ferns we tumble into this 
abyss. 
It is true that our knowledge of certain Palaeozoic forms which 
appear in many respects to be more primitive than (or at least as 
primitive as) any existing Ferns has greatly increased of late years. 
But the Botryopterideae and their allies, as we shall see in some 
detail in the next lecture, certainly fall within our concept of 
“Ferns,” and though it is held (and with much reason) that they 
stand in some respects close to the ancestors not only of several 
existing groups of Ferns, but also of the fossil Pteridosperms, 
yet they scarcely help us at all with the question “ From what 
kind of plant were the Ferns derived ? ” No forms have yet 
been found in any respect truly intermediate between Ferns, or 
any Pteridophytic group, and the lower plants, whether Bryophytes 
or Thallophytes. 
There is much reason to believe that the true vascular plants 
had a common origin—in other words that the Pteridophyta are a 
monophyletic group. Otherwise we should have to suppose that 
the evolution of roots, those characteristically constructed and very 
uniform organs of vascular plants, as well as of the whole typical 
histological apparatus of the vascular system, fundamentally of the 
same type throughout the Pteridophyta, and also of the structure of 
the sexual organs, is homoplastic on at least two lines of descent. 
These would be very large assumptions, which could not be justified 
