SPORANGIOPHORE A PART SUI GENERIS 133 
attached to an axis would thus be held to be a complete. foliar structure, 
and a sporangiophore attached to the upper surface of a bract would be 
recognised as a “ventral lobe” of that bract. But if it be admitted that 
spore-production in the sporophyte was prior to its vegetative development, 
and was a constant phase throughout the evolution of the sporophyte, 
then such a description seems not only unnecessary but highly improbable. 
Moreover, it has been seen that sporangiophores may be present in positions. 
which are not those-of the normal succession of known vegetative parts ;. 
in the endeavour ‘to bring these into line with the customary position and 
succession of vegetative parts, recourse has to be taken to almost fantastic 
explanations. But there is no need for this if the sporangiophore be accepted 
simply to be, what it structurally is, a placental growth. The object of 
the morphologist should be not the forcible reduction of different organisms 
to one scheme of construction, but to read in their diverse forms the 
probably diverse story of their origin. This should proceed along the. lines 
of the least strained and simplest interpretation. Following these principles, 
the sporangiophore in the Pteridophytes will be held to be a part suz 
generis, itself primitive in its nature, in the sense that it is not the result 
of modification or replacement of any other sort of appendage. 
Certain physiological limitations must necessarily have been operative 
during the transition of the fertile region of any sporophyte from a simpler 
to a more complex condition, such as has been figured to the mind in 
the last chapter. As already pointed out, an increase in spore-production 
is an advantage in homosporous plants, since it increases the chance of 
survival and of distribution. But in any increasing body the formation 
of separate loculi will facilitate the protection and nutrition of the increasing 
mass of spores while young: thus segregation has its biological rationale. 
Projection of the sporangia beyond the surface of the part which produces. 
them will facilitate the shedding of the spores, and makes possible those 
mechanical devices which are seen in so many of the Pteridophytes. For 
the protection of the sporangia while young, close juxtaposition of the 
appendages -of the strobilus is also important, and illustration of this is 
seen in almost all strobiloid types. But at the same time any projection 
" of the spore-producing parts necessitates the conveyance of their nourish- 
ment through a longer distance, and by more restricted channels. Such 
crossing of interests will have tended to keep the appendages which bear 
the spores small, so long as they are themselves not active or essential as 
nutritive organs; in fact, there would in that case be a tendency to. per- 
petuate the strobiloid type. But if the. appendages themselves carry on 
efficiently the function of supply of organic material, then there need be 
no limit to their size, provided that the water-supply to them can be 
maintained; and they may accordingly bear an infinity of sporangia, as is 
seen to be the case in the megaphyllous types. It is in connection with 
these functions of protection and nutrition that the foliar development 
would. naturally come into prominence as a feature of ‘the. strobilus, and 
