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 tissue 

 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, Kaitlfussia, 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. 1 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 



1 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). 



