INTRODUCTORY ON PTERIDOPHYTA 289 
study of the Bryophytes. Nor, on the other hand, does it justify the 
initial assumption that the origin of the sporophyte in Vascular Plants 
differed essentially from that in the Bryophytes. Accordingly, the theory 
of progressive sterilisation will here be applied to the study of the 
Pteridophytes also, along lines parallel to those observed for the Bryo- 
phytes. It is not to be expected that the facts will amount to a complete 
demonstration : the present object will be to see how far they accord with 
a theory which has its more obvious application in the simpler series of 
Archegoniate Plants. 
The most important evidence will naturally be obtained from the study 
of the spore-producing members themselves; and these will be described 
in detail in the several types of Pteridophytes. But facts of value bearing 
indirectly on the general hypothesis, are also to be derived from the form 
and structure of the vegetative parts, as well as from their origin and 
early development. In fact, the whole sporophyte is to be studied in 
relation to the question of its origin, just as much in the more complex 
as in the simpler Archegoniate forms. One guiding line must constantly 
be maintained, and it is this: that however late in the individual life the 
production of spores may appear, still spore-production was on our general 
hypothesis the first office of the sporophyte. By various means the vege- 
tative phase may have attained a large size, and~ great complexity of 
structure: but however preponderant it may appear, still we should be 
prepared to regard it theoretically as secondary, that is, as a phase 
intercalated between the events of nuclear fusion in the zygote and 
reduction in the spore-mother-cell. 
It will be well to observe some regular order in the discussion of 
the large area of fact involved. The several groups of the Pteridophytes 
will accordingly be taken in succession, starting from those with relatively 
small appendages and strobiloid habit, and proceeding to those with 
appendages of larger size. The fossil representatives will be included in 
the discussion, together with the living forms. In each group a pre- 
liminary section will deal with the extermal characters of the mature 
organism, with special reference to the balance of the vegetatiye and 
reproductive regions. It will be followed by a detailed examination of 
the spore-producing members, and lastly, certain facts of anatomy and 
of embryology will be considered in their bearings on the general ques- 
tion. The characters of the gametophyte will only be referred to 
incidentally, so far as they affect the biological circumstances of the 
young sporophyte. 
If then the Pteridophyta be arranged according to the coniplexity of 
the appendages, and especially of their spore-producing parts, the Lycopodiales 
will come first, since in them each isolated sporangium is attached in the 
_median plane to its subtending sporophyll. 
A second series is characterised by having one or more sporangia 
borne on a vascular pedicel: when the number is more than one they 
T 
