152 SPORANGIOPHORES AND SPOROPHYLLS 
Spore-bearing bodies, or sporangiophores, or sori such as. those above 
named, have then the following characters in common: They are out- 
growths of varying length, which bear one or more sporangia: these are, 
when numerous, more or ‘less closely related one to another, and frequently 
synangial: they are usually disposed in a circle round the periphery of a 
disc-like expansion at the distal end of the more or less elongated stalk. 
but other arrangements may be found. A vascular strand usually runs 
through the stalk to its distal end, where it may divide into’ branches 
which terminate in close relation with the sporangia. The similarity in 
all essentials of structure of the sporangiophores in these early Pteridophytes, 
notwithstanding the diversity of their position, points to the conclusion that 
they are the result of similar response to similar requirements, carried out, 
it may be, in various distinct stocks in the various positions in which 
they are now seen. Their structure suggests that they are simply the 
outcome of placental growth, which has the advantage of securing freedom 
of dehiscence of the sporangia which they bear. In that case there is no 
obligation to hold that they were the result of “metamorphosis” of any 
pre-existent appendage or part. And herein lies the importance! of the 
introduction of the term sforangiophore which is now applied to them; 
for it simply implies the fact that the part so called bears sporangia, but 
does not suggest any view of its further morphological character, nor does 
it impose any limitation upon the position which the. sporangiophores 
may hold. 
It remains to consider what relation, if any, subsists between such 
sporangiophores and the “leaves.” The difficulty in finding mutual ground 
for discussion of this question lies in the preconceived ideas which the term 
“leaf” carries with it in the minds of many botanists. It is often assumed 
that the vegetative leaf was pre-existent in descent to the appendages of 
the strobilus, the mind naturally translating the successive events of : the 
individual life directly into the history of its evolutionary organisation ; in 
fact, the sporophyll has habitually been regarded as a vegetative leaf which 
has become fertile. In the following chapter reasons will be given for 
holding that the converse is nearer the truth, ze. that foliage leaves are 
often the equivalent of sporophylls which have become in the course of 
descent sterile. If this be so, then signs of the origination of a vegetative 
system are to be sought .in the fertile zone rather than the converse. 
A second preconception which is commonly entertained is that “the 
leaf,” whether sporophyll or foliage leaf, is a part having a common 
evolutionary origin in all plants in which it appears;. but on grounds 
explained above. we .shall be prepared to contemplate as possible a 
polyphyletic origin of those parts which are’ designated collectively 
“leaves.” a : 5 cs 
. A third preconception, which is a common one also, is that those 
bodies which are designated sporangiophores. are necessarily of the nature 
of sporophylls, or of segments or parts of sporophylls. Any sporangiophore 
