698 CONCLUSION 
But the objection may be raised that the vascular supply has also to 
be accounted for. It is a general experience in the plant-body that vascular 
development follows demand: and many examples might be quoted both 
from vegetative and propagative organs. It appears that similarly a 
vascular supply extended into the synangium; a first indication of such a 
development is seen occasionally in the sporangia of Lycopodium (Fig. 161), 
while it is a common feature in the megasporangia of Seed-Plants. Thus 
any objection to a theory of origin of the sporangiophore by a process of 
septation and outgrowth on the ground of the presence of vascular tissuc 
does not appear to be valid. Moreover, such vascular extension is seen 
in less full development in those sporangiophores where the sporangia are 
obliquely erect and synangial, as in the Psilotaceae, ‘Kazlfussta, and 
Ptychocarpus (Fig. 288), but further developed where they are inverted 
and separate, as in the Equisetales. It has already been argued that the 
former are the less advanced, and those with separate and inverted 
sporangia the more advanced types (pp. 426-7). 
It is thus seen that there is coincidence between sporangia and 
sporangiophores in their leading function of spore-production : that there is 
commonly a similarity of position of the two: that either may undergo fission 
independently of the subtending bract, that in certain sporangia there are 
indications of partial septation, and occasionally a technically complete 
septation: also that the facts of development of the synangial sporangio- 
phores harmonise in varying degree with a theory of origin from a non- 
septate sporangial sac. The conclusion, therefore seems justified that they 
are essentially comparable parts, the one being the simpler, the other the 
more complex terms of a category of phyletically uniform organs. That 
the non-septate sporangium was the more primitive there can be little 
doubt. So far as palaeontological evidence bears upon the question, 
Lycopodinous types with their non-septate sporangia appear to have been 
fully as early as any of the more elaborate forms. 
Turning now to the Ferns, which had been temporarily put aside while 
discussing the strobiloid types. It has been accepted as probable that the 
soral condition was the original state in Ferns, and the non-soral 
derivative (p. 633), while it was left an open question whether the sori 
were originally marginal or superficial in their position upon the 
sporophyll (p. 634). It has also been pointed out how close the structural 
similarity is between certain synangial sori and the sporangiophores of the 
smaller-leaved types (pp. 151, 524). It may have been the fact that this 
striking similarity was a result of parallel development, but still it would 
appear probable that the evolutionary progressions which produced them 
were of a like kind. There is ample evidence also of fission of sori in 
Ferns (pp. 511, 555, 620), essentially like that of the sporangiophores of 
the strobiloid types. It would therefore appear probable that the condition 
'The designation of sporangiophores as ventral or other lobes of the sporophyll has 
been objected to on a previous page, and reasons given for its rejection (p. 426). 
