132 G. R. Wieland — Cycadeoidean Flower-hud Structure. 



Salisbury* have introduced an elaborate and very usable ter- 

 minology for the seed apices. But this should not mislead us 

 into reading into these structures undue complexity of origin. 

 For Oliver and Salisbury themselves in their paper on the 

 Affinities of the Paleozoic seeds of the Conostoma group, just 

 cited, explicitly describe a continuity of the tissues in the 

 Lagenostome region : " * * Thus we see that the epidermal 

 layer of the interior of the seed is in complete continuity 

 throughout and that the various regions termed the micro- 

 pylar tube* micropylar funnel, plinth jacket, plinth, and lag- 

 enostome tvalls are merely different and specialized portions 

 of o?ie and the same layer." The italics are mine and in my 

 judgment this continuity does permit and does suggest as the 

 most reasonable hypothesis the origin of the seed wall from 

 eared fronds like the units which go to make up the Cyca- 

 deoidea disk, by a simple process of sterilization and reduction 

 in the case of most Paleozoic seeds. Certainly it is possible 

 that the Cycadeoidean or similar disks are very ancient struc- 

 tures, and that a theory of reduction from such disks as the 

 result of sterilization and megaspore protection by reduced 

 fronds, rests under less burden of demonstration than does any 

 theory of seed coat origin which calls into requisition much 

 direct evolution of new structures. Especially so when the 

 particular structures from which such evolution could have 

 proceeded are now seen to be but hypothetical at best. 



Furthermore, reproduction being so completely dependent 

 on nutritive processes primarily and on the use of protective 

 coverings secondarily, it is certain that as megaspores increased 

 in size, the simplest mode of protection would be inside a 

 whorl of leaves at the center of a more or less scaly bud or 

 crown. And alike in the Devonian as in the Mesozoic t'he 

 development of apical domes would best overcome the spatial 

 requirements due to circinate or conduplicate prefloration. 

 At least this is the explanation that comes first to hand, it 

 being clear enough that such an outer covering would at once 

 enable the plant to greatly increase the size of its megaspores, 

 protect them in an economical manner from insects, rain and 

 wind, and then, following the assumption of microphylly with 

 later cycles of branching and budding, greatly increase the 

 number of fruits. So I conceive the seed habit was made pos- 

 sible and acquired by a process of reduction and sterilization 

 with final enclosure of a giant apical spore after the forward 

 course of evolution which first enabled plants to invade and 

 cover the land and then raise their stems above the soil, had 

 culminated. 



*Aun. Bot., vol. xxv, No. xcvii, Jan., 1911. 



